The History of Timekeeping

Egyptian star tables on coffin lids (c. 2100 BC) (c. 2100 BC)

The oldest known attempt to tell the time at night is a grid of star names painted on the inside of Egyptian coffin lids. Egyptologists call them diagonal star tables, because the same star names step down the grid in a diagonal pattern. Each of 36 columns stood for a ten-day 'week' of the 365-day civil year, and each row marked a star group, or decan, rising later in the night. Watching which decan had just come up over the eastern horizon told an observer roughly how far the night had run.

How it was made: The tables first appear on coffins of the First Intermediate Period and early Middle Kingdom, most of them from the cemetery at Asyut. By about the 21st century BC the decans were being used as a sidereal night clock.

Where it is now: Star tables were mostly a coffin decoration of this period, but the decans outlived them, appearing for example on the astronomical ceiling of Senenmut's tomb. They passed into later Egyptian sky diagrams such as the Dendera zodiac, then into Greek astrology, where they gave way to the twelve signs of the zodiac.

• The Greeks called the decans 'dekanoi', meaning 'tenths', because a new one appeared at dawn every ten days.
• Historian Sarah Symons counts about 27 tables, depending on how fragments are counted; only one is not on a coffin, painted instead on a temple ceiling.
• Symons argues the 'hours' they mark were shorter than 60 minutes and uneven, so she prefers to call them star tables rather than star clocks.

Try it yourself: A planisphere, the modern dial for finding which stars are rising tonight (planisphere star finder on Amazon)

Sources: Museo Egizio, Turin: inner face of the coffin of Iqer, with a diagonal star clock; Scientific American: Decoding the star charts of ancient Egypt; Wikipedia: Decan

Sixty minutes and twenty-four hours (from c. 2000 BC) (c. 2000 BC to AD 150)

Two ancient habits are still on every clock face. The Sumerians counted in base 60, and the Babylonians used it for their astronomy; 60 divides evenly by 2, 3, 4, 5, 6, 10, 12, 15, 20 and 30. The Egyptians split daylight into 12 parts and the night into 12 more, which gave a 24-hour day. Much later, Ptolemy's Almagest (about AD 150) cut each degree into 60 small parts and those again into 60, and those 'first' and 'second' small parts became our minutes and seconds.

How it was made: Base-60 counting began with the Sumerians, probably in the third millennium BC, and passed to the Babylonians. Egyptian sundials and star tables supplied the twelve-part day and night, and the Greek astronomer Hipparchus proposed 24 equal hours based on the equinox.

Where it is now: It never ended. Ordinary people kept seasonal hours of changing length for centuries, and equal hours only became normal in Europe after mechanical clocks spread in the 14th century; minute hands for everyday use came near the end of the 16th.

• The Latin name for the first sixtieth was 'partes minutae primae', the 'first small parts', which became 'minute'; the second division became the 'second'.
• The scholar al-Biruni divided the hour into sixtieths around AD 1000, and John of Sacrobosco did the same around 1235, helping fix hours, minutes and seconds.
• The seven-day week is often credited to Babylon, but the evidence is thin: Babylonians marked the 7th, 14th, 21st and 28th days of each lunar month, while a continuous seven-day cycle is first known from Judaism.

Sources: Yale Babylonian Collection YBC 7289, an Old Babylonian tablet written in base 60 (ISAW exhibition record); Scientific American: Why is a minute divided into 60 seconds, an hour into 60 minutes?; Wikipedia: Sexagesimal; Wikipedia: Week

Egyptian shadow clock (c. 1500 BC) (c. 1500 BC)

The shadow clock is the oldest kind of sundial. A raised crossbar, turned to face the sun, cast its shadow along a marked base. One portable type divided the sunlit day into ten parts plus two 'twilight hours'. Because daylight was always split into the same number of parts, an hour in summer was longer than an hour in winter.

How it was made: An L-shaped bar found in the tomb of Thutmose III (reigned 1479-1425 BC) appears to be one, and a ceiling text in Seti I's cenotaph at Abydos gives spacings of 3, 6, 9 and 12 units for marking such a bar. The surviving examples are simple carved stone or wood.

Where it is now: Shadow clocks were overtaken by hemispherical and flat Greek and Roman sundials, but the basic design lasted a very long time: the Science Museum says simple versions were still used in Egypt in the early 20th century.

• In 2013 a University of Basel team reported a limestone dial with a painted half-circle in 12 sections of about 15 degrees, near workmen's huts in the Valley of the Kings, dated to the 13th century BC.
• The Science Museum in London holds a wooden shadow clock from Qus, made around 1000-800 BC and over a metre long.
• For night hours the Egyptians used the merkhet, a sighting tool; one in the Science Museum, given by Howard Carter, names its owner as Bes, an astronomer-priest of Horus at Edfu.

Try it yourself: A brass garden sundial, the same shadow-reading idea in a modern form (brass garden sundial on Amazon)

Sources: Science Museum Group: Ancient Egyptian altitude sundial, or shadow clock (1926-992); Science Museum Group: Egyptian merkhet (1929-585); NIST: A walk through time, early clocks; North American Sundial Society: New insights into ancient sundials; NBC News (2013): Egyptian sundial kept time in 13th century BC

The Karnak water clock (c. 1390 BC) (c. 1390-1352 BC)

A water clock measures time by water running out of, or into, a marked vessel, so it works at night and under cloud. The oldest one that survives is an alabaster bowl made under Amenhotep III and used at the temple of Amun-Re at Karnak. Water leaked from a small hole near the base, and the falling level was read against scales cut inside. There are twelve scales, one for each month, because the Egyptian night hours changed length through the year.

How it was made: Simple outflow bowls were used in Egypt, Babylon and Persia by around the 16th century BC. A tomb inscription of a 16th-century BC court official, Amenemhet, even names him as its inventor.

Where it is now: The Karnak clock was found at Karnak in 1904 and is now in Cairo. Water clocks themselves stayed in use for some 2,000 years, growing gears and dials in Greek, Chinese and Islamic hands.

• The Greeks called the water clock 'clepsydra', and Greek and Roman courts used outflow clepsydrae to limit how long a speaker could talk.
• NIST notes that another early water clock was found in the tomb of Amenhotep I, buried around 1500 BC.
• Scholar Rita Gautschy has asked whether it was really a working timer or mainly a costly votive gift to the god.

Sources: Science Museum Group: cast of the Karnak water clock of Amenhotep III; Rita Gautschy (2020): The Karnak clepsydra, votive gift or utilitarian object? (University of Basel); NIST: A walk through time, early clocks; Wikipedia: Water clock

Rome's first public sundial (263 BC) (263 BC)

According to Pliny the Elder, citing the scholar Varro, the first sundial set up for the Roman public was brought from Catana (modern Catania) in Sicily during the First Punic War. The consul Manius Valerius Messalla placed it on a column near the Rostra in the Forum in the year of Rome 491, our 263 BC. It had been laid out for a latitude further south, so its lines did not match Rome's hours, but Romans lived by it for 99 years. Before that, an official simply called out midday when he saw the sun between the Rostra and the Graecostasis.

• Pliny reports an even earlier claim, from the writer Fabius Vestalis, that Lucius Papirius Cursor put a sundial at the temple of Quirinus about 30 years before, but says no one recorded how it was made.
• The censor Quintus Marcius Philippus finally set a properly drawn dial beside the old one, and Pliny says Romans counted it one of the best acts of his censorship.
• Since sundials failed in cloudy weather, Scipio Nasica later set up a public water clock that divided night as well as day, in the year of Rome 595 (159 BC).

Sources: Pliny the Elder, Natural History 7.60, trans. Bostock and Riley (Project Gutenberg, vol. 2); Smith's Dictionary of Greek and Roman Antiquities (1875): Horologium (LacusCurtius); Wikipedia: Manius Valerius Maximus Messalla

The Antikythera mechanism (c. 150-100 BC) (c. 150-100 BC)

The Antikythera mechanism is a Greek bronze calculator with at least 30 surviving gears, once housed in a wooden case. Its gears drove displays that tracked the Sun and Moon through the zodiac, predicted eclipses, and followed long calendar cycles such as the Metonic and Saros. It is not a clock, but it is the oldest known geared machine for computing time and the sky. Nothing as complex is known for roughly a thousand years after it.

How it was made: Sponge divers from Symi found a wreck off the island of Antikythera in 1900, and the mechanism came up in 1901. In 1902 a gear wheel was spotted in one lump of corroded bronze, and the museum director, Valerios Stais, began the first study of it.

Where it is now: The ship sank around 70-60 BC, and the device survives as 82 fragments in the National Archaeological Museum in Athens. X-ray scans in 2005 revealed its hidden gearing, and the team published its reading in Nature in 2006.

• One dial tracked the four-year cycle of the Greek athletic games, including the Olympics.
• Its gears reproduce the Moon's speeding up and slowing down along its orbit, the irregularity described by the astronomer Hipparchus.
• Its date is still argued: estimates run from about 205 BC to 87 BC, and a 2022 study proposed a starting calibration of 23 December 178 BC.

Try it yourself: A desk replica of the Antikythera mechanism's gearwork (Antikythera mechanism replica model on Amazon)

Sources: National Archaeological Museum, Athens: The Antikythera Mechanism; ScienceDaily (2006): report on the Cardiff-led study published in Nature; Wikipedia: Antikythera mechanism

Tower of the Winds, Athens (c. 50 BC) (by c. 50 BC)

The Tower of the Winds is an eight-sided marble building in Athens that served as a public timekeeper. Each face carries a carved figure of one of the eight winds and a sundial, and a water clock fed from a spring on the Acropolis ran inside, so the hour could be read at night or under cloud. On the roof a bronze Triton swung with the breeze and pointed his rod at the wind that was blowing. The Roman scholar Varro called it the Horologium.

How it began: Vitruvius and Varro credit the astronomer Andronicus of Cyrrhus. The date is not recorded; architectural style points to the 2nd or 1st century BC, and Varro mentions it around 37 BC.

What became of it: The water clock and the Triton are lost, but the tower stands. It may have served as a church in late antiquity, became a dervish tekke in the 1750s, and was restored and reopened to visitors in 2016.

• Vitruvius used the tower as proof that there are eight winds, not four, and described how the Triton turned to face the breeze.
• Dervishes used the building for rituals from the 1750s until 1821, when it was abandoned during the Greek revolt.
• Only channels cut in the floor remain of the water clock, and how it showed the hours is still uncertain.

Try it yourself: Vitruvius's Ten Books on Architecture, the Roman text that describes the tower and its water clocks (Vitruvius Ten Books on Architecture on Amazon)

Sources: Vitruvius, The Ten Books on Architecture, Book I ch. 6 (Project Gutenberg); World History Encyclopedia: Tower of the Winds; Smith's Dictionary of Greek and Roman Antiquities (1875): Horologium (LacusCurtius); Wikipedia: Tower of the Winds

Su Song's astronomical clock tower (1088) (1088)

Su Song's clock tower, about 12 metres tall, was a water-powered astronomical machine built for the Song emperor at Kaifeng. A large water wheel advanced in steps, held and released by a weighing mechanism that worked as an escapement, the device that lets stored energy out in small regular amounts. Through an endless chain drive it turned an armillary sphere on the roof and a celestial globe inside. Small figures appeared at doors with plaques and struck bells, gongs and drums to announce the time.

How it was made: Su Song (1020-1101), a scholar-official, led the project; a wooden pilot model was finished in 1088 and the tower by 1094. His illustrated description, the Xinyi Xiangfayao, was written in 1092.

Where it is now: After the Song capital moved south in 1127 the tower was taken apart, and attempts to rebuild it failed. Su Song's book survived, and the historian Joseph Needham studied it closely in the 20th century.

• The water-driven escapement idea in China goes back to about AD 725, the work of Yi Xing and Liang Lingzan.
• Its chain drive, the 'celestial ladder', is often called the oldest known endless power-transmitting chain.
• The Science Museum built 1:48 and 1:6 scale models in 1965, and says the find challenged the idea that mechanical clocks were invented only in Europe.

Sources: Science Museum Group: scale model of Su Song's water-balance escapement (1965-8); Science Museum Group: model of a Chinese astronomical clock tower (1965-7); NIST: A walk through time, early clocks; Wikipedia: Su Song

Al-Jazari and his book of ingenious devices (1206) (1206)

Ismail al-Jazari was chief engineer to the Artuqid rulers in upper Mesopotamia. In 1206 he finished The Book of Knowledge of Ingenious Mechanical Devices, which describes fifty machines with instructions for building them. Its water clocks and candle clocks used floats, pulleys and automata to mark the hours, among them the famous elephant clock and a 'castle clock' about 3.4 metres high. Because he explained construction step by step, modern engineers have been able to rebuild his designs.

How they rose: Al-Jazari was born in 1136 in the Jazira, the land between the Tigris and Euphrates, and served the court as his father had. The ruler Nasir al-Din Mahmud commissioned the book.

How they died: He died in 1206, the year the book was completed. The earliest known copy of his book is in the Topkapi Palace Library in Istanbul.

• His castle clock showed the zodiac, and every hour doors opened to reveal figures, while five automaton musicians played.
• The historian Donald Hill judged his candle clocks the most sophisticated known, noting they used a bayonet fitting.
• One device in the book measured blood let during medical bloodletting, with seated scribe figures indicating the amount; the Science Museum holds a 1977 reconstruction.

Try it yourself: An English edition of al-Jazari's book of machines and clocks (al-Jazari Book of Knowledge of Ingenious Mechanical Devices on Amazon)

Sources: Science Museum Group: copy of al-Jazari's bloodletting measuring device (1981-1710); Science Museum Group: Ismail ibn al-Razzaz al-Jazari (biography); Wikipedia: Ismail al-Jazari

The verge-and-foliot escapement (c. 1300) (late 1200s to early 1300s)

Every mechanical clock needs an escapement, a device that lets the power of a falling weight or a spring out a little at a time. The first in Europe was the verge with a foliot: a crown-shaped wheel pushed a pair of small flags on an upright rod, rocking a horizontal bar with weights on its ends back and forth. Moving the weights in or out made the clock run slower or faster. Weight-driven clocks of this kind appeared in the towers of Italian cities in the first half of the 14th century, and in English cathedrals by its end.

How it was made: No one knows who invented it. In 1271 the astronomer Robertus Anglicus wrote that clockmakers were still trying to make one, and by the late 13th or early 14th century it existed; written records are muddied because 'horologium' meant any timekeeper, water clocks included.

Where it is now: Pendulums, from 1656, and the anchor escapement soon replaced it in clocks, and most surviving foliot clocks were converted. Verge watches stayed common until the lever escapement took over in the mid-19th century.

• Estimates of early verge clocks' error range from one to two hours a day, though modern experiments suggest careful builds could keep within minutes.
• The Dover Castle clock in the Science Museum, made in London around 1632-40 and found at the castle in 1872, is one of the few public clocks still regulated by its original foliot.
• Giovanni de' Dondi's 1364 drawings include one of the earliest known pictures of a verge, using a wheel-shaped balance instead of a foliot bar.

Try it yourself: A skeleton clock that shows its escapement and gear train in motion (skeleton mechanical wall clock on Amazon)

Sources: Science Museum Group: Dover Castle turret clock with original foliot (1884-81); NIST: A walk through time, a revolution in timekeeping; Wikipedia: Verge escapement

Richard of Wallingford, God's clockmaker (1327) (1327-1336)

Richard of Wallingford was an Oxford-trained monk who became abbot of St Albans in 1327. That year he wrote the Tractatus Horologii Astronomici, the first clear written description of a mechanical astronomical clock. His clock struck the hours and showed the Sun and Moon, the phases of the Moon, and the height of the tide at London Bridge. He also designed calculating instruments, including an equatorium called the Albion.

How they rose: Born around 1292 in Wallingford, the son of a blacksmith, he was orphaned young and raised at Wallingford Priory, a dependency of St Albans. He studied at Oxford before returning to the abbey.

How they died: He suffered from a disease then thought to be leprosy and died at St Albans in 1336, aged about 44. William of Walsham finished the clock some 20 years later; it was probably destroyed when the abbey was dissolved in 1539.

• The 16th-century antiquary John Leland praised the clock as one of the finest in Europe.
• Richard's treatise survives in the Bodleian Library's Ashmole MS 1796; the historian John North edited and translated it in 1976, which made modern reconstructions possible.
• The Whipple Museum in Cambridge holds a quarter-size working replica built by Don Unwin in 1992, because a full-size one would not fit in a museum gallery.

Try it yourself: John North's God's Clockmaker, the biography of Richard of Wallingford (God's Clockmaker John North on Amazon)

Sources: Whipple Museum, Cambridge: quarter-size replica of Richard of Wallingford's clock; Linda Hall Library: Scientist of the Day, Richard of Wallingford; MacTutor (St Andrews): St Albans, Hertfordshire; Wikipedia: Richard of Wallingford

The hourglass (first pictured 1338) (1338)

Nobody knows who invented the hourglass. The earliest firm evidence is a detail in Ambrogio Lorenzetti's Allegory of Good Government, painted in 1338-39 in Siena's Palazzo Pubblico, where Temperance holds a sandglass. Soon afterwards sandglasses appear in ship stores, because sand, unlike water, was not upset by a rolling deck. Sailors used them to time watches and, with a log line, to measure a ship's speed.

How it was made: Guinness World Records notes that the device probably emerged in the 11th or 12th century, from Islamic or European makers, but the 1338 fresco is the first concrete proof. Early glasses were two separate bulbs bound together with cord and wax.

Where it is now: Mechanical clocks made hourglasses less common after 1500, and marine chronometers replaced them for navigation. They survive as kitchen timers, game timers and desk ornaments.

• The earliest written record that surely means a marine sandglass is a receipt of about 1345 for twelve glass 'horologes' bought in Flanders for Edward III's ship La George.
• Magellan's fleet carried 18 hourglasses from Barcelona.
• The story that an 8th-century monk named Luitprand invented the hourglass has no evidence behind it, and many old glasses held powdered marble or burnt eggshell rather than sand.

Try it yourself: A one-hour glass sand timer, the medieval sailor's clock for a desk (hand blown glass hourglass sand timer 60 minute on Amazon)

Sources: Ambrogio Lorenzetti, Allegory of Good Government (1338-39), Fondazione Musei Senesi via Google Arts & Culture; Guinness World Records: First hourglass; Wikipedia: Marine sandglass; Wikipedia: Hourglass

Giovanni de' Dondi's astrarium (1364) (1348-1364)

The astrarium was a weight-driven astronomical clock about a metre tall, built in Padua by the physician Giovanni de' Dondi. Above a 24-hour dial and a calendar drum, seven dials showed the Sun, the Moon and the five planets then known, following Ptolemy's model of the heavens. Its roughly 107 wheels and pinions were held together by more than 300 tapered pins and wedges rather than screws. Dondi wrote such a full description that the lost machine could be rebuilt six centuries later.

How it was made: Dondi, whose father was also a clockmaker in Padua, began work in 1348 and finished in 1364. The work made him famous as 'Giovanni dall'Orologio', Giovanni of the Clock.

Where it is now: In 1381 Dondi gave the astrarium to Gian Galeazzo Visconti, who installed it in his castle library at Pavia, where it is recorded until at least 1485; after that its fate is unknown. Dondi died in 1388.

• The calendar drum had no leap-year allowance; Dondi's advice was to stop the clock for a whole day.
• His treatise, the Tractatus astrarii, survives in about twelve manuscripts, including his own autograph in the Biblioteca Capitolare in Padua.
• At least eight replicas have been built since the 1960s, including one made by Thwaites and Reed in 1974 for the Science Museum in London.

Try it yourself: A brass orrery, a geared desk model of the planets in the astrarium's spirit (brass orrery solar system desk model on Amazon)

Sources: Science Museum Group: reconstruction of Dondi's astronomical clock (1974-386); Linda Hall Library: Scientist of the Day, Giovanni Dondi; Wikipedia: Astrarium of Giovanni Dondi dall'Orologio

Salisbury and Wells cathedral clocks (c. 1386-1392) (c. 1386 and 1392)

Salisbury Cathedral's clock is an iron-framed tower clock with no dial; its job was to strike a bell on the hour. It is usually dated to about 1386 from a deed of that year mentioning the bell tower that housed it. Its sister clock from Wells Cathedral, dated 1392, now sits in the Science Museum in London, while its painted dial remains in the cathedral. Both were originally regulated by a foliot and later converted to pendulums.

How it began: Their makers are unknown. A 2018 study by Keith Scobie-Youngs argued that the Salisbury, Wells and Rye clocks came from the same maker, and that Rye's is the oldest of the three.

What became of it: The Salisbury clock was found in the tower in 1928 by the horologist T.R. Robinson and restored in 1956 by John Smith & Sons of Derby, who removed its pendulum and fitted a reproduction verge and foliot. It still runs in the cathedral.

• Guinness World Records lists Salisbury's as the world's oldest surviving working clock, saying it struck the hours for nearly five centuries before its 1956 restoration.
• At a 1993 symposium most experts judged the Salisbury clock original, but about a third thought it much later; its advanced construction resembles 16th- and 17th-century clocks.
• Rival 'oldest clock' claims come from Beauvais in France, Chioggia in Italy and Comayagua in Honduras.

Sources: Science Museum Group: Wells Cathedral clock, 1392 (1884-77); Guinness World Records: Oldest clock; MacTutor (St Andrews): Salisbury, Wiltshire; Wikipedia: Salisbury Cathedral clock

The Prague astronomical clock (1410) (1410)

The Prague orloj on the south wall of the Old Town Hall is a mechanical clock with an astronomical dial showing the Sun and Moon against the sky, plus several kinds of time at once. Its oldest parts, the mechanism and the astronomical dial, are dated to 1410 and credited to the clockmaker Mikuláš of Kadaň and the astronomer Jan Šindel of Charles University. A calendar dial was added below later, and on the hour a skeleton rings a bell while figures of the apostles pass two windows. The outer ring counts Old Czech time, in hours from sunset.

How it began: The 1410 date rests on archival evidence put forward by the historian Zdeněk Horský; a 1459 record confirms the dial was working. Around 1490 a Master Hanuš improved it and added a calendar plate.

What became of it: In the Prague uprising of May 1945 German fire burned the Old Town Hall, the wooden figures and the calendar dial. Repaired by 1948, the clock was restored again in 2018, when its 1948 electric drive was replaced by a mechanism in its 1860s form.

• The famous story that city councillors blinded the clockmaker Hanuš so he could never build another is a legend, popularised by the writer Alois Jirásek; crediting the clock to Hanuš was a historical mistake later corrected by Horský.
• The apostle figures were added after a major repair in 1787-1791; the ones seen today were carved by Vojtěch Sucharda after the 1945 fire.
• The painter Josef Mánes designed the calendar dial, which was replaced by a copy in 1880.

Sources: Rijksmuseum: 19th-century albumen print of the astronomical clock by F. Friedrich & K. Preuss (RP-F-F16054); Prague City Tourism: Historie pražského orloje (in Czech); Hyperallergic: The history of one of the oldest astronomical clocks in the world; Wikipedia: Prague astronomical clock

Peter Henlein and the 'Nuremberg egg' (c. 1511) (c. 1511)

Peter Henlein was a Nuremberg locksmith who made small spring-driven timepieces that could be carried on the body. In 1511 the scholar Johannes Cochlaeus praised 'Peter Hele', still a young man, for clocks of iron with many wheels that ran for 40 hours without a weight and struck the hours while worn on the chest or in a purse. That makes him one of the earliest named makers of portable clocks. Calling him the inventor of the watch, though, is a 19th- and 20th-century legend; mainsprings existed before him.

How they rose: Born in Nuremberg around 1485, he was caught up in a 1504 killing during a brawl among locksmiths and sheltered in the Franciscan monastery until 1508. He became a master locksmith in 1509.

How they died: He died in Nuremberg in 1542. In 1524 the city council bought from him a gilded musk-apple (a pomander) containing a clock, for 15 gulden.

• The oval 'Nuremberg eggs' were not his: egg-shaped watches became fashionable decades after his death, and the name likely comes from wordplay on 'Ührlein', German for 'little clock', which sounds like 'Eierlein', 'little egg'.
• Research in 2013-14 showed that the Germanisches Nationalmuseum's 'Henlein watch', long called the oldest pocket watch in the world, was assembled in the 19th century from some period parts.
• Nuremberg marked the supposed 400th anniversary of the pocket watch in 1905 with a fountain in his honour, and a 1939 German film, The Immortal Heart, told his story.

Try it yourself: A hand-wound mechanical pocket watch, the descendant of the first wearable clocks (mechanical hand wind skeleton pocket watch on Amazon)

Sources: Germanisches Nationalmuseum: 'Henlein watch', wrongly attributed to Peter Henlein (Google Arts & Culture); Deutsche Biographie (NDB/ADB): Henlein, Peter; Wikipedia: Peter Henlein; Wikipedia: Nuremberg egg

The Gregorian calendar (1582) (24 February 1582)

The Julian calendar assumed a year of 365 and a quarter days, about 11 minutes too long, and over the centuries the spring equinox, and with it Easter, had drifted about ten days early. Pope Gregory XIII's bull Inter gravissimas, dated 24 February 1582, removed ten days from October 1582 so that 4 October was followed by 15 October. It also changed the leap-year rule: century years are leap years only if divisible by 400, so 1700, 1800 and 1900 were not, but 1600 and 2000 were. The scheme was worked out by Aloysius Lilius and, after his death, by the Jesuit mathematician Christopher Clavius.

• The major Catholic powers switched at once; Protestant countries mostly waited until the 18th century, and Greece, in 1923, was the last European country to change.
• Britain and its colonies switched in 1752, by then needing to drop eleven days: Wednesday 2 September was followed by Thursday 14 September.
• The famous 'give us our eleven days' riots are probably exaggerated; the slogan appears on a banner in William Hogarth's An Election Entertainment, painted about three years later.

Sources: Inter gravissimas (1582), English translation (Wikisource); Royal Museums Greenwich: William Hogarth, An Election Entertainment (print); Linda Hall Library: Scientist of the Day, Pope Gregory XIII; History (UK): The calendar riots of 1752; Wikipedia: Inter gravissimas

Galileo and the pendulum (1583-1642) (c. 1583-1642)

Galileo Galilei studied pendulums and found that the time of one swing stays nearly the same whether the swing is wide or narrow, and depends on the pendulum's length, not its weight. That property, called isochronism, is what makes a pendulum a good regulator for a clock. His earliest surviving report of pendulum experiments is a letter of 29 November 1602. In 1641, old and blind, he described to his son Vincenzo a way to keep a pendulum swinging and count its beats.

How they rose: The famous origin story, that the young Galileo timed a swinging lamp in Pisa Cathedral with his pulse around 1583, comes from his pupil Vincenzo Viviani's biography, written in 1654 and printed in 1717. The Museo Galileo treats it as tradition.

How they died: Galileo died in 1642 without a working clock. Vincenzo began building one but died in 1649 before finishing it; the first successful pendulum clock was Christiaan Huygens's in 1656.

• The historian Antonio Favaro showed that the lamp shown to visitors in Pisa Cathedral was installed after Galileo left Pisa; another votive lamp from his time survives in the city's Monumental Cemetery.
• Galileo's isochronism holds only for small swings; Huygens later proved that a truly constant period needs a pendulum moving along a cycloid.
• The Science Museum's model of Galileo's clock, made in Florence by Eustachio Porcellotti in 1883 from Viviani's drawing, is called the first known attempt to control a clock with a pendulum.

Try it yourself: Galileo's Two New Sciences, where he set out his findings on motion and the pendulum (Galileo Two New Sciences Dover on Amazon)

Sources: Science Museum Group: pendulum clock designed by Galileo, model (1883-29); Museo Galileo: Viviani's Racconto istorico della vita di Galileo; Museo Galileo: Cathedral of Santa Maria, Pisa (the lamp tradition); Royal Holloway: Galileo and the pendulum clock; Wikipedia: Pendulum

Huygens's pendulum clock (1656) (December 1656)

In December 1656 the Dutch scientist Christiaan Huygens made the first successful pendulum clock by coupling a swinging pendulum to a clock's escapement, so the pendulum's steady beat set the pace. The best clocks before it drifted by about 15 minutes a day; pendulum clocks could keep to about 15 seconds. Huygens saw that wide swings run slightly slow and added curved 'cheeks' at the suspension to correct it. His Horologium Oscillatorium of 1673 gave the full mathematics of the pendulum.

How it was made: In 1657 Huygens gave Salomon Coster, a clockmaker in The Hague, the sole right to make his clocks in the Netherlands, and published the design in Horologium in 1658. By 1659 pendulum clocks were being made in France and England.

Where it is now: The pendulum clock ruled precision timekeeping for nearly three centuries, until quartz clocks took over in the 1930s and 1940s. Coster's 1657 clock survives in the Rijksmuseum Boerhaave in Leiden.

• The oldest surviving pendulum clock is signed 'Salomon Coster Haghe met privilege 1657', the 'privilege' being Coster's licence from Huygens.
• Huygens's Horologium Oscillatorium showed that only a pendulum swinging along a cycloid keeps exactly the same time for every swing.
• Once clocks could keep time to seconds, the minute hand became worthwhile, and minute hands became common on clock faces around 1690.

Try it yourself: A key-wound mechanical pendulum clock, Huygens's idea on a living-room wall (Hermle mechanical pendulum wall clock on Amazon)

Sources: Christiaan Huygens, Horologium oscillatorium (Paris, 1673), Internet Archive; Science Museum Group: early pendulum clock by Salomon Coster, c. 1657 (1980-108); Science Museum Group: Christiaan Huygens (biography); Guinness World Records: Oldest pendulum clock; Wikipedia: Pendulum clock

The balance spring (1675) (1675)

A watch cannot use a pendulum, so its rate is set by a balance wheel swinging back and forth. Before 1675 the balance had nothing to give it a natural rhythm, and watches could wander by hours a day. In 1675 Christiaan Huygens fitted a fine spiral spring to the balance, giving it a steady period of its own; watches improved to roughly ten minutes a day, and a minute hand on a watch finally made sense. Every mechanical watch still has one.

How it was made: Huygens had the Paris clockmaker Isaac Thuret make watches with his spiral spring. In London, Robert Hooke claimed he had found the idea first and, later in 1675, had Thomas Tompion make balance-spring watches under his direction.

Where it is now: The priority quarrel was never settled, and Thuret also claimed credit. Balance springs were nearly universal in portable timekeepers until quartz movements displaced them from the 1980s, though they remain the heart of every mechanical watch.

• The Science Museum's early balance-spring watch by Tompion, made in 1675-79, already shows minutes with a large central hand and has a separate seconds dial.
• Hooke and Tompion fell out bitterly in 1675; Hooke called the clockmaker a 'slug', and the reason for the quarrel is unknown.
• Tompion's regulator for adjusting the spring, from around 1680, was the first to be widely used.

Try it yourself: A skeleton mechanical watch, so you can watch the balance and its spring breathe (skeleton mechanical watch exhibition caseback on Amazon)

Sources: Science Museum Group: early balance spring watch by Thomas Tompion (1985-1537); Science Museum Group: Thomas Tompion (biography); NIST: A walk through time, a revolution in timekeeping; Wikipedia: Balance spring

Royal Observatory, Greenwich (1675) (4 March 1675)

The Royal Observatory was founded to map the stars precisely enough for sailors to find their longitude at sea. Charles II signed a warrant on 4 March 1675 appointing John Flamsteed his 'astronomical observator', a post later called Astronomer Royal. Christopher Wren, helped by Robert Hooke, designed the building on the old foundations of Greenwich Castle. Two year-going clocks by Thomas Tompion, commissioned by Sir Jonas Moore, were accurate enough for Flamsteed to show that the Earth turns at a steady rate.

How it began: A French visitor, the Sieur de St Pierre, claimed in December 1674 to have a lunar method for longitude; English scholars rejected it in February 1675, and the royal warrant for an observatory followed in March. Flamsteed laid the foundation stone on 10 August 1675 and moved in on 10 July 1676.

What became of it: London's smoke and light pushed the scientific work out to Herstmonceux in Sussex, a move completed in 1957. The Greenwich site is now a museum run by Royal Museums Greenwich.

• Flamsteed House cost £520, which was £20 over budget, and because it reused old foundations it points about 13 degrees away from true north.
• Tompion's two great clocks for Flamsteed had pendulums about 13 feet (4 m) long, hung behind the panelling of the Great Room, now the Octagon Room; each swing took two seconds.
• A time ball on the roof has dropped at 1 pm every day since 1833 so ships on the Thames could set their chronometers, and in 1884 the meridian through Greenwich was adopted as the world's prime meridian.

Sources: Royal Museums Greenwich: The Royal Observatory from Crooms Hill, about 1696 (painting); Royal Museums Greenwich: Year-going clock by Thomas Tompion, 1676; Royal Museums Greenwich: The founding of the Royal Observatory; Wikipedia: Royal Observatory, Greenwich

The Longitude Act (1714) (July 1714)

Sailors could find their latitude from the Sun and stars, but not how far east or west they were, and ships were lost because of it. In July 1714 Parliament passed 'An Act for Providing a Publick Reward for such Person or Persons as shall Discover the Longitude at Sea'. It offered £10,000 for a method accurate to within one degree of longitude, £15,000 within 40 minutes, and £20,000 within 30 minutes. A body of Commissioners, later called the Board of Longitude, judged the claims.

• The Act was prompted by a 1713 proposal from William Whiston and Humphrey Ditton, and Isaac Newton and Edmund Halley advised the committee on the accuracy required.
• The full £20,000 was never paid as one prize; John Harrison received £23,065 in total over many years, the largest sum the Board paid anyone.
• Other rewards went to the widow of the astronomer Tobias Mayer (£3,000) and to Leonhard Euler (£300) for the rival lunar-distance method; the Board was dissolved in 1828 after paying out over £100,000.

Sources: Cambridge University Library / Royal Museums Greenwich: An Act for Providing a Publick Reward ... (1714, RGO 14/1), extract and transcription; Royal Museums Greenwich: Harrison's clocks and the longitude problem; Wikipedia: Longitude rewards

Thomas Mudge and the lever escapement (c. 1755) (c. 1755)

Thomas Mudge devised the detached lever escapement in the 1750s, first applying it to a clock. In a lever escapement a small pivoted lever unlocks the escape wheel and gives the balance a push, then leaves the balance swinging freely for most of its arc, which makes the watch more accurate and less sensitive to wear. Mudge used it in only a handful of pieces, most famously a watch George III bought for Queen Charlotte around 1770. Refined by others over the next century, it became the standard: since about 1900 virtually every mechanical watch has used a lever escapement.

How they rose: Born in Exeter in 1715, Mudge was apprenticed in London to George Graham, Thomas Tompion's successor, and set up his own business at 151 Fleet Street. He was a respected maker of complicated watches before the lever.

How they died: Ill health sent him to Plymouth in 1771, where he spent his later years on marine timekeepers; in 1792 a House of Commons committee awarded him £2,500. He died on 14 November 1794 at his son's house in Newington Butts, south London.

• Mudge supplied Dr Samuel Johnson's first watch in 1768 and was appointed watchmaker to George III in 1776.
• Queen Charlotte's lever watch is still in the Royal Collection at Windsor Castle.
• After his death his son paid other makers to build chronometers to his design; they cost £157 each, did not perform as well, and only about 15 were made.

Try it yourself: A hand-wound field watch, ticking on a modern Swiss lever escapement (Hamilton Khaki Field Mechanical on Amazon)

Sources: Science Museum Group: gold lever escapement watch by John Leroux, 1785, with notes on Mudge's invention; Royal Museums Greenwich library: A description, with plates, of the time-keeper invented by the late Mr Thomas Mudge (1799); Science Museum Group: Thomas Mudge (biography); Science Museum Group: marine timekeeper to Mudge's design by Howells & Pennington, 1795; Wikipedia: Thomas Mudge (horologist); Wikipedia: Lever escapement

John Harrison's H4 sea watch (1759) (1759)

John Harrison spent three decades building sea clocks to win the longitude prize. His first three, H1 to H3, were large brass machines; H4, finished in 1759, was a watch about 13 centimetres across, weighing 1.45 kg. Its fast, heavy balance ticked five times a second and shrugged off a ship's motion. On a trial voyage to Jamaica in 1761-62 it was only five seconds slow after 81 days, an error of about one nautical mile in longitude.

How it was made: Harrison, born in Yorkshire in 1693, was a carpenter who taught himself clockmaking; by the mid-1720s his longcase clocks kept time to about a second a month. He finished H1 in 1735, and in 1736 it sailed to Lisbon and back, helping to correct the ship's navigation on the return.

Where it is now: The Board of Longitude doubted the trials, and Harrison fought it for years; George III himself tested the follow-up watch H5 in 1772. Harrison died in London on 24 March 1776, and H4 is in the collection of Royal Museums Greenwich.

• On a second trial to Barbados in 1764, H4 kept time to within 39 seconds, an error of under 10 miles; the Board put the result down partly to luck.
• A copy of H4 made by Larcum Kendall, known as K1, went with Captain James Cook on his second and third Pacific voyages.
• The clocks lay neglected until the naval officer Rupert Gould restored them, unpaid, after the First World War; he was the first to call them H1 to H5.

Try it yourself: Dava Sobel's Longitude, the classic account of Harrison's quest (Longitude Dava Sobel book on Amazon)

Sources: Royal Museums Greenwich: H4 (marine timekeeper), object record; Royal Museums Greenwich: H1 (marine timekeeper), object record; Royal Museums Greenwich: Harrison's clocks and the longitude problem; NIST: A walk through time, a revolution in timekeeping; Wikipedia: John Harrison

Breguet of Paris: from the perpétuelle to the tourbillon (1775-1801) (1775-1801)

Abraham-Louis Breguet, born in Neuchâtel in 1747, founded his workshop in Paris in 1775 and became the most inventive watchmaker of his age. By about 1783 he was making 'perpétuelle' watches that wound themselves as the wearer moved. On 26 June 1801 he patented the tourbillon, which carries the escapement and balance in a rotating cage so that errors caused by a watch hanging in one position average out. His customers included Louis XVI, Marie Antoinette and Napoleon.

How it began: Breguet trained in France and supplied the royal court before the Revolution. He fled to Switzerland and then England in its most dangerous years, returning to Paris around 1795.

How it ended: Breguet died in 1823 and the business continued as Breguet et Fils; in 1870 the watchmaking side was sold to an English retailer. The Breguet name lives on as a watch brand.

• The Princess de Valençay paid 1,600 francs for a Breguet one-minute tourbillon watch in 1812; it is now in the Clockmakers' Museum collection in London.
• Fewer than a thousand tourbillons are thought to have been made between 1801 and 1945, often for observatory trials.
• The entire Breguet collection of Sir David Salomons was among 106 timepieces stolen from a Jerusalem museum in 1983; the thief was identified in 2006, and by 2008 all but ten of the stolen items had been recovered.

Try it yourself: Emmanuel Breguet's illustrated history of the house his ancestor founded (Breguet Watchmakers Since 1775 Emmanuel Breguet book on Amazon)

Sources: Science Museum Group: early 'perpétuelle' watch by Abraham-Louis Breguet, c. 1783 (L2015-3292); Science Museum Group: one-minute tourbillon watch by Breguet sold to the Princess de Valençay, 1812; Science Museum Group: Breguet et Fils (company record); Wikipedia: Tourbillon; Wikipedia: Abraham-Louis Breguet

Patek Philippe (1839) (1839 to today)

Antoni Patek and Franciszek Czapek founded Patek, Czapek & Cie in Geneva on 1 May 1839. In 1844, at the Paris Industrial Exposition, Patek came across the work of Jean Adrien Philippe, who had devised a watch wound and set by its stem instead of a separate key. Philippe joined in 1845 and the firm became Patek, Philippe & Cie in 1851. Over the next century it built a run of firsts, including what is usually called the first perpetual calendar wristwatch, in 1925.

How it began: Patek was the businessman and Philippe the inventor; Philippe had devised his keyless winding system in 1842, and his patents were filed from 1845. The 1851 renaming put both names on the dial.

How it ended: Charles and Jean Stern bought the company in 1932, during the Depression, and the Stern family still owns it. It is based in Plan-les-Ouates, outside Geneva, and calls itself the last independent family-owned watch manufacture in the city.

• Queen Victoria bought a Patek keyless pendant watch at London's Great Exhibition in 1851.
• The Henry Graves Supercomplication, a gold pocket watch with 24 complications delivered in January 1933, sold at Sotheby's Geneva on 11 November 2014 for CHF 23,237,000 with fees. It had sold in 1999 for 11 million dollars.
• For the firm's 150th anniversary in 1989 it made the Calibre 89, a pocket watch with 33 complications. Only four were built.

Sources: Patek Philippe: The founders (company history); SJX Watches: The technical evolution of Patek Philippe; Sotheby's: Patek Philippe's four most complicated watches; Monochrome Watches: Graves Supercomplication sets record at Sotheby's; Wikipedia: Patek Philippe

Railway time on the Great Western (1840) (November 1840)

In November 1840 the Great Western Railway set its whole timetable by London (Greenwich) time, the first recorded case of one standard time applied across places with different local times. Until then every town kept its own sun time, so Bristol's clocks ran about ten minutes behind London's and Exeter's about fourteen. A timetable that changed time at every station was unworkable, and other lines followed. In 1847 the Railway Clearing House told its member railways to adopt Greenwich time, and by the mid-1850s almost every public clock in Britain showed it.

• Bristol's Exchange clock was given a second minute hand, one showing local time and one showing London time.
• Exeter held out until 2 November 1852, when it changed after a meeting between the city council and the cathedral authorities.
• Greenwich time was used everywhere for decades before it was law: Parliament made it Britain's legal time only with the Statutes (Definition of Time) Act of 1880.

Sources: legislation.gov.uk: Statutes (Definition of Time) Act 1880; Royal Museums Greenwich: Greenwich Mean Time; NIST: A Walk Through Time, world time scales; Wikipedia: Railway time

Waltham and the American system (1850) (1850 to 1957)

In 1850 Aaron Lufkin Dennison and clockmaker Edward Howard set out to make watches by machine, with parts cut so precisely that any one would fit any watch of the same model. After a cramped start in Roxbury, the firm moved to a new factory in Waltham, Massachusetts, in 1854. Under the Waltham name it turned the watch from a hand-finished luxury into a factory product. Between 1850 and 1957 the company made about 40 million watches, clocks, speedometers, compasses and other instruments.

How it began: Dennison, a watch repairman, raised 20,000 dollars of starting capital with Howard and partners. The business was renamed the Boston Watch Company in 1853, and the Waltham plant opened in 1854 with 90 workers making about 30 watches a week.

How it ended: The original company went out of business in 1957. After several bankruptcies and restarts, the Waltham name is now held outside North America by a Swiss company, which still makes mechanical watches under it.

• At the 1876 Philadelphia Centennial Exposition Waltham showed its automatic screw-making machinery and won the first gold medal in a watch precision contest.
• The Swiss sent engineer Jacques David, later director of Longines, to study Waltham and Elgin. His report of more than 100 pages warned that Swiss watchmaking would be destroyed unless it mechanised, and it stayed unpublished until Longines issued a facsimile in 1992.
• Swiss watch exports to the United States reportedly fell from over 18 million francs in 1872 to under 5 million by 1876.

Try it yourself: A hand-wound mechanical pocket watch, the kind Waltham turned into a factory product (mechanical hand wind pocket watch on Amazon)

Sources: Jacques David, American and Swiss Watchmaking in 1876 (translated report, R. Watkins); Antique Pocket Watch: 1876, the Centennial Exhibition and the American System; Wikipedia: Waltham Watch Company

Shepherd's Greenwich master clock (1852) (1852)

In 1852 the Astronomer Royal, George Airy, installed an electric 'motor' clock made by Charles Shepherd at the Royal Observatory, Greenwich. It sent an electrical pulse every second to slave dials around the Observatory and drove the time signals sent by telegraph to London, Edinburgh, Glasgow, Dublin, Belfast and other cities. From 1866 its signals also crossed the Atlantic by submarine cable to Harvard University. One of its dials, set in the Observatory gate, was the first clock to show Greenwich Mean Time directly to the public.

How it was made: Shepherd had shown a connected clock system at the Great Exhibition of 1851, and Airy ordered one for Greenwich. Charles Shepherd Junior had patented his electric clock improvements in 1849, at the age of 19.

Where it is now: The motor clock stayed at the centre of Britain's time distribution until 1893. It survives in the Royal Museums Greenwich collection, though not on display; the gate clock still works, driven by a quartz mechanism, and shows GMT all year without changing for summer time.

• The gate clock has a 24-hour dial, so at noon its single hour hand points straight down.
• A bomb damaged the gate clock's dial on 15 October 1940; the mechanism survived and the dial was replaced with an exact copy.
• Shepherd estimated 40 pounds for the motor clock and time-ball apparatus; the motor clock alone ended up costing 70 pounds and the gate clock 75.

Sources: Royal Museums Greenwich: Electrical motor clock (ZAA0531); Royal Museums Greenwich: The Shepherd gate clock; NIST: A Walk Through Time, world time scales; Wikipedia: Shepherd Gate Clock

The Day of Two Noons (1883) (18 November 1883)

At noon on 18 November 1883, railroads across the United States and Canada switched to four standard times, based on the 75th, 90th, 105th and 120th meridians west of Greenwich. Until then each town kept its own sun time; the US had more than 300 local times, and the railroads had tried about 100 railway times of their own. In the eastern part of each new zone, clocks reached local noon and were then set back, so the town heard noon twice. Congress did not make the zones law until March 1918.

• Congress had considered and rejected a national standard time in 1809, 1870 and 1872, so the railroads simply did it themselves.
• William F. Allen, who drew up the railroad plan, told the 1884 International Meridian Conference that the system had proved satisfactory and that the railways wanted no further change.
• Not everyone was pleased: some people complained that standard time robbed them of daylight or went against nature.

Sources: Protocols of the International Meridian Conference, 1884 (Project Gutenberg), including W. F. Allen's remarks; Union Pacific Railroad Museum: Standard time; NIST: A Walk Through Time, world time scales; Wikipedia: Time in the United States

International Meridian Conference (1884) (October 1884)

The conference opened in Washington, D.C., on 1 October 1884, with 41 delegates from 26 countries. It recommended the meridian through the transit instrument at the Greenwich observatory as the world's prime meridian for longitude, and a universal day counted from zero to twenty-four hours. Only San Domingo voted against Greenwich; France and Brazil abstained. Greenwich was already the practical choice: the US had based its railroad time zones on it, and about 72 percent of the world's shipping used charts based on it.

• France kept Paris mean time as its legal time until 1911.
• The conference also passed a resolution hoping that studies of decimal time and decimal angles would be resumed.
• Sandford Fleming, the great Canadian champion of standard time, sat with the British delegation representing the Dominion of Canada.

Sources: Protocols of the Proceedings, International Meridian Conference, 1884 (Project Gutenberg); Royal Museums Greenwich: Greenwich Mean Time; NIST: A Walk Through Time, world time scales; Wikipedia: International Meridian Conference

The Kipton wreck and railroad watch rules (1891) (April 1891)

In April 1891 a fast mail train and a westbound passenger train of the Lake Shore and Michigan Southern Railway collided head-on at Kipton, Ohio, about 40 miles west of Cleveland. Investigators found that the passenger conductor's watch had stopped for about four minutes and then started again, so his train was late reaching the siding where it should have let the mail train pass. Accounts give the date as 18 or 19 April and the dead as eight or nine. The railroad hired Cleveland jeweler Webb C. Ball to study its timekeeping, and the inspection system he built set the pattern for railroad watches across North America.

• Ball's rules covered resistance to magnetism, accurate running in five positions, isochronism and power reserve, and each watch's record was updated at every scheduled inspection.
• By the end of his career Ball oversaw timekeeping on more than 125,000 miles of track in the United States, Mexico and Canada.
• The Ohio historical marker at Kipton credits Ball's insistence on accuracy for the saying 'get on the ball'. It is a good story; treat it as local legend rather than proven word history.

Sources: Ohio History Connection marker 24-47: Great Kipton Train Wreck; PBS History Detectives: Map to the famous train crash site; Wikipedia: Webb C. Ball

Cartier Santos (1904) (1904)

The story, told by Cartier ever since, is that in 1904 the Brazilian aviator Alberto Santos-Dumont complained to his friend Louis Cartier that he could not check a pocket watch while flying. Cartier answered with a flat, square watch on a strap. It is often called the first pilot's watch. Cartier began selling the 'Santos-Dumont' to the public around 1911, with movements from a predecessor of Jaeger-LeCoultre.

How it was made: Santos-Dumont was a celebrity in Paris, famous for his airships and early aeroplanes, and Cartier moved in the same circles. The exact watch he wore has been lost, so its design is known from surviving early examples.

Where it is now: Cartier reinvented it in 1978 as a sports watch, sometimes on a steel bracelet, and the Santos is still in the Cartier range.

• On 19 October 1901 Santos-Dumont flew his airship No. 6 around the Eiffel Tower in 29 minutes 30 seconds; the judges first refused him the 100,000-franc Deutsch Prize and then gave in.
• On 12 November 1906 his 14-bis aeroplane flew 220 metres at Bagatelle, a flight recognised by the Aero-Club de France.
• The exposed screws on the Santos bezel are sometimes read as a nod to aircraft rivets, though that is an interpretation, not a documented design brief.

Sources: Santos-Dumont, My Airships (1904), Project Gutenberg; Gear Patrol: Watches you should know, the Cartier Santos; Cigar Aficionado: Time flies (pilot watches); Wikipedia: Alberto Santos-Dumont

Trench watches (1914) (1914 to 1918)

When the First World War began, British officers were expected to buy their own wristwatch, and makers sold 'campaign' or 'service' watches to suit. The most prized feature was a luminous dial, painted with radium so it glowed in a dark trench; according to the watch historian David Boettcher, wristwatches were not made with luminous dials before 1914. A 1916 officer's handbook, Knowledge for War, put a 'luminous wristwatch with unbreakable glass' first on its kit list, ahead of the revolver. By 1917 the Horological Journal noted the wristlet watch on the wrist of nearly every man in uniform.

How it was made: Soldiers first strapped small pocket watches into leather holders called wristlets. Purpose-made men's wristwatches appeared from around 1900, and British officers had worn wrist-mounted watches on India's North West Frontier since the 1880s.

Where it is now: The word 'wristlet' gave way to 'wristwatch' in the early 1930s. Radium paint stopped glowing well after about three years but stays radioactive, so surviving dials are handled as hazards.

• At a 1916 company meeting the jeweller H. Williamson Ltd claimed that one soldier in four wore a wristlet watch, an unverified boast but a sign of how fast the habit spread.
• In 1915 J. W. Benson sold silver trench watches on leather straps from 2 pounds 2 shillings, at a time when a lieutenant earned 8 shillings 6 pence a day.
• The Science Museum holds a 1915 Ingersoll wristwatch with a luminous hour hand; its catalogue entry lists it as radioactive material.

Sources: Science Museum Group: Ingersoll wrist watch with luminous hour hand, 1915 (1987-1035); Vintage Watchstraps (David Boettcher): Trench watches; Wikipedia: Trench watch

Daylight saving time begins (1916) (30 April 1916)

On 30 April 1916 Germany and Austria-Hungary put their clocks forward an hour, the first nationwide daylight saving time. Britain followed with the Summer Time Act, starting on 21 May 1916, a year after the death of William Willett, who had campaigned for it since his 1907 pamphlet The Waste of Daylight. The United States adopted it in 1918. Today about a third of the world's countries use it, mostly in Europe and North America.

• The first serious proposal came in 1895 from George Hudson, a New Zealand entomologist who wanted a two-hour shift.
• Port Arthur and Fort William in Ontario became the first cities to adopt daylight saving, on 1 May 1908.
• In the Second World War Britain used Double Summer Time, two hours ahead of GMT, and from 1968 to 1971 it kept its clocks forward all year.

Sources: legislation.gov.uk: Summer Time Act 1916; Royal Museums Greenwich: British Summer Time and daylight saving; NIST: Daylight saving time; Wikipedia: Daylight saving time

Shortt-Synchronome free pendulum clock (1921) (1921)

William Hamilton Shortt invented his clock in 1921 with the horologist Frank Hope-Jones, and Hope-Jones's Synchronome Company in London built it. It used two pendulums: a master swinging in a vacuum tank with almost no work to do, and a slave pendulum in a separate clock that drove the hands and triggered a gentle push to the master every 30 seconds. It quickly replaced Riefler's clocks as the top timekeeper in observatories and remained the world's best standard from the 1920s into the 1940s.

How it was made: Shortt's key contribution was the electromechanical link that kept the slave pendulum in step with the untouched master.

Where it is now: About 100 were made between 1922 and 1956 before quartz clocks took over. Royal Museums Greenwich keeps Shortt clock No. 3 on display at the Royal Observatory.

• In 1926 a Shortt clock detected tiny seasonal changes in the Earth's rotation, making it arguably the first clock more stable than the Earth.
• It is usually quoted as accurate to about a second a year; a 1984 study found it stable to about a second in 12 years.
• The Riefler clock it replaced, from 1889, was itself good to about a hundredth of a second a day.

Sources: Royal Museums Greenwich: Shortt Free Pendulum System No. 3, slave clock (ZAA0539.1); NIST: A Walk Through Time, a revolution in timekeeping; Wikipedia: Shortt-Synchronome clock

The self-winding wristwatch: Harwood to Rolex (1923) (1923 to 1931)

John Harwood, a watch repairer from Bolton, filed a British patent on 7 July 1923 and a Swiss one that October for a wristwatch wound by a pivoting weight. Spring bumpers stopped the weight after about 180 degrees, and with no winding crown the hands were set by turning the bezel. Fortis of Grenchen began making Harwood watches in 1926. In 1931 Rolex patented its Perpetual rotor, a half-moon weight that could turn a full 360 degrees and stored enough energy for up to 35 hours, against about 12 for Harwood's.

How it was made: Self-winding pocket watches had existed since Abraham-Louis Perrelet's of 1776 or 1777, but a pocket watch barely moves. Harwood saw that a wristwatch, swinging all day, was the right home for the idea.

Where it is now: Harwood's own company failed in 1931, starved of money in the Depression, after about 30,000 watches had been made. The full rotor became the industry standard, refined by Eterna's ball-bearing rotor in 1948.

• A 1777 report to a Geneva society said 15 minutes of walking would fully wind Perrelet's self-winding watch.
• Fortis, which made the first Harwood automatics, had been founded in Grenchen in 1912 by Walter Vogt.
• Harwood took out his British patent together with a financial backer, Harry Cutts.

Try it yourself: A watch winder keeps a self-winding watch running while it is off your wrist (automatic watch winder on Amazon)

Sources: Science Museum Group: Harwood self-winding wrist-watch (1968-677); Europa Star: Fortis marks the centenary of the Harwood; Wikipedia: Automatic watch

Rolex Oyster and the Channel swim (1926) (1926)

Hans Wilsdorf, who had founded his firm in London in 1905 and moved it to Geneva in 1919, launched the Oyster case in 1926. Its bezel, case back and winding crown all screwed down against the middle of the case to keep water and dust out. The crown design came from Georges Perret and Paul Perregaux, whose rights Wilsdorf bought; the US patent, filed in 1926 and granted in 1928, was assigned to him. In October 1927 the British swimmer Mercedes Gleitze wore an Oyster in the English Channel, and on 24 November Rolex launched the watch in Britain with a front-page advertisement in the Daily Mail.

How it was made: Wilsdorf registered the Rolex name in 1908 and had already won chronometer certification for a small wristwatch in 1910. A watch that survived water was the next proof that a wristwatch could be a serious tool.

Where it is now: The screw-down Oyster case is still the basis of the Rolex range. Since Wilsdorf's death in 1960 the company has been owned and run by the Hans Wilsdorf Foundation.

• The patent describes a winder that screws onto a threaded part of the case to form a tight joint, linked to the stem by a pin and slot so it can still be pulled out to set the hands.
• Gleitze's own Oyster sold at Sotheby's Geneva on 9 November 2025 for about 1.7 million dollars, above its estimate.
• Gleitze later said the watch had proved a reliable and accurate timekeeping companion.

Try it yourself: Seiko 5 Sports: an affordable water-resistant automatic for everyday wear (Seiko 5 Sports automatic watch on Amazon)

Sources: Google Patents: US1661232A, Keyless watch (Perret, assigned to Wilsdorf); National Jeweler: Historic Rolex Oyster fetches 1.7M at Sotheby's; Wikipedia: Rolex

The first quartz clock, Bell Labs (1927) (1927)

In 1927 Warren Marrison and J. W. Horton at Bell Telephone Laboratories built the first quartz clock. A quartz crystal, which vibrates at a steady rate when electrified, produced pulses at 50,000 cycles a second; Marrison divided that frequency down electronically until it could drive a synchronous clock motor. He was trying to count the crystal's vibrations to measure frequency, and found he had made a clock. A refined version followed in 1928.

How it was made: Marrison, born in Inverary, Ontario, in 1896, served as a radio technician in the Royal Flying Corps, studied at Queen's University and Harvard, and joined Bell Labs in 1925. His frequency-control patent was filed on 28 March 1927.

Where it is now: During the 1940s time laboratories around the world switched from pendulums to quartz, until atomic clocks overtook it. Shrunk to a chip, the same principle runs today's quartz watches.

• The patent, US 1,788,533, was granted on 13 January 1931 and assigned to Bell Telephone Laboratories.
• A 1929 New York Times headline announced that an electrified quartz crystal had displaced the clock pendulum.
• Marrison was inducted into the National Inventors Hall of Fame in 2011, more than 30 years after his death in 1980.

Try it yourself: Timex Weekender: an inexpensive quartz watch, the pocket-sized heir of Bell Labs' crystal clock (Timex Weekender watch on Amazon)

Sources: Google Patents: US1788533A, Frequency-control system (Marrison); National Inventors Hall of Fame: Warren Marrison; NIST: A Walk Through Time, a revolution in timekeeping; Wikipedia: Warren Marrison

First caesium atomic clock, NPL (1955) (1955)

In 1955 Louis Essen and Jack Parry at the National Physical Laboratory in Teddington built the first practical caesium atomic frequency standard. It measured time by a change of state in caesium atoms and was accurate to about one second in 300 years, roughly 300 times better than the best pendulum clocks. It did not run continuously; it was used every few days to check a quartz clock.

How it was made: An earlier atomic clock built in the US in 1949, based on ammonia, was not much better than existing standards. Essen, who had built a quartz ring clock at NPL in 1938, turned to caesium instead.

Where it is now: The original clock is in the Science Museum in London. By 1960 caesium standards were part of official timekeeping, and in 1967 caesium became the definition of the second.

• Essen was also a sceptic of Einstein: in 1971 he published a critique of special relativity's treatment of time.
• The Soviet Academy of Sciences awarded him its A. S. Popov Gold Medal in 1959.
• In 1946 Essen measured the speed of light with a microwave cavity; his refined 1950 value was adopted internationally in 1957.

Sources: Science Museum Group: Caesium atomic clock, 1955 (1962-59); Physics World: A brief history of timekeeping; NIST: A Walk Through Time, the atomic age of time standards; Wikipedia: Louis Essen

The atomic second (1967) (1967)

In 1967 the 13th General Conference on Weights and Measures defined the second as the duration of 9,192,631,770 periods of the radiation from a particular transition in the caesium-133 atom. It replaced the 'ephemeris second' chosen in 1956, which was based on the Earth's orbit. For the first time the basic unit of time came from a laboratory, not from astronomy. Every atomic clock, GPS satellite and phone network now counts in these seconds.

• NIST's caesium fountain NIST-F1, the eighth in its line of caesium clocks, could keep time to about 30 billionths of a second a year by 2002.
• In 1997 the standards committee added that the definition refers to a caesium atom at rest at absolute zero.
• The best caesium fountains now reach about one part in 10 to the 16th, but only after averaging for several days.

Sources: BIPM: Resolution 1 of the 13th CGPM (1967), SI unit of time (second); NIST: A Walk Through Time, the atomic age of time standards; Physics World: A brief history of timekeeping; Wikipedia: Second

Omega Speedmaster on the Moon (1969) (21 July 1969)

Omega launched the Speedmaster in 1957 as a sports and racing chronograph. Wally Schirra wore his own on the Mercury flight Sigma 7 in October 1962, and NASA later put commercial chronographs through eleven tests, from heat and vacuum to shock and vibration, choosing the Speedmaster in 1965. On 21 July 1969 Buzz Aldrin wore his on the lunar surface; Neil Armstrong left his inside the lunar module as a backup, because the module's electronic timer had failed. It became known as the Moonwatch.

How it was made: NASA announced that the Speedmaster was qualified for human spaceflight in 1965, and that June Ed White wore one on the first American spacewalk during Gemini 4.

Where it is now: The hand-wound Speedmaster Professional is still made, now with the co-axial Calibre 3861 introduced in 2021. It is still described as the only watch NASA has qualified for spacewalks.

• Aldrin's Moon watch was lost in the post when he sent it to the Smithsonian, and has never been found.
• On Apollo 13 Jack Swigert used his Speedmaster to time a critical 14-second engine burn, and the astronauts gave Omega a Snoopy Award in 1970.
• The Smithsonian holds 63 Speedmasters; 55 flown chronographs were formally accepted from NASA in the spring of 1977.

Try it yourself: The Omega Speedmaster Professional Moonwatch, still made and still flight-qualified (Omega Speedmaster Professional Moonwatch on Amazon)

Sources: Science Museum Group: Omega Speedmaster watch, NASA type (1977-817/1); Smithsonian National Air and Space Museum: Space, time and technology; Wikipedia: Omega Speedmaster

Seiko Quartz-Astron 35SQ (1969) (25 December 1969)

Seiko introduced the Quartz-Astron 35SQ in Tokyo on 25 December 1969, the first quartz wristwatch sold to the public. Its crystal vibrated 8,192 times a second, a hybrid integrated circuit counted the vibrations, and a tiny stepping motor moved the hands. It was accurate to within five seconds a month, about a minute a year. The first watches had 18-carat gold cases and cost 450,000 yen, about 1,250 dollars, roughly the price of a mid-sized car.

How it was made: The watch came out of about ten years of work at Suwa Seikosha by a team led by Tsuneya Nakamura. Seiko had worked on quartz clocks since 1958, and a portable Seiko quartz chronometer served as a backup timer at the 1964 Tokyo Olympics.

Where it is now: About 100 sold in the first week. Within a few years cheap quartz watches flooded the market and set off the Swiss quartz crisis.

• The Astron's crystal ran at 8,192 Hz, a quarter of the 32,768 Hz used in most quartz watches today.
• The IEEE named the Astron a Milestone in 2004; its plaque hangs at the Seiko Institute of Horology in Tokyo.
• Seiko's launch slogan claimed that someday all watches would be made this way.

Try it yourself: Seiko's current Astron line: solar-powered watches that set themselves by GPS (Seiko Astron GPS Solar watch on Amazon)

Sources: Deutsches Uhrenmuseum Furtwangen: Seiko Quartz Astron movement, cal. 35A, 1969 (museum-digital); IEEE (ETHW) Milestone: Electronic Quartz Wristwatch, 1969; Gear Patrol: The Seiko quartz watch that broke Switzerland; Wikipedia: Astron (wristwatch)

Hamilton Pulsar LED watch (1970) (1970 (on sale 1972))

Hamilton introduced the Pulsar, the first electronic digital wristwatch, in 1970, reportedly on Johnny Carson's Tonight Show. It went on sale in spring 1972 in an 18-carat gold case for 2,100 dollars. Quartz kept the time and a red light-emitting diode display showed it, but the LEDs drew so much power that the screen stayed dark until you pressed a button. The Science Museum calls it the first watch without any moving parts.

How it was made: Hamilton developed it with Electro/Data Inc. of Garland, Texas, using CMOS chips supplied by RCA. It was designed in the United States and went into large-scale production in 1972.

Where it is now: Battery-hungry LEDs were soon overtaken by liquid-crystal displays. Seiko bought the Pulsar brand in 1978, and Hamilton now sells the PSR, a tribute marking the original's fiftieth anniversary.

• Roger Moore's James Bond wears a Pulsar in Live and Let Die (1973).
• The Computer History Museum keeps a 1970 Pulsar 'Wrist Computer' as an early consumer product built on CMOS chips.
• Seiko merged the Pulsar brand into its ALBA line in January 2023.

Try it yourself: Hamilton's PSR, a modern tribute to the 1970 Pulsar (Hamilton PSR digital quartz watch on Amazon)

Sources: Computer History Museum: Digital watch with LED display, Hamilton, 1970 (X979.89); Science Museum Group: 'Pulsar' digital quartz wristwatch with LED display, 1972 (1984-35); Hamilton: American Classic PSR Digital Quartz (H52414130); Wikipedia: Pulsar (watch)

The quartz crisis (1970s to 1980s) (1970 to 1988)

Before the 1970s Swiss watchmakers held about half the world market. Then cheap quartz watches from Japan and Hong Kong, more accurate than any mechanical watch, swept in. The number of Swiss watch firms fell from about 1,600 in 1970 to about 600 by 1983, and employment fell from about 90,000 in 1970 to 47,000 by 1980 and 28,000 by 1988. The two largest Swiss groups, SSIH and ASUAG, were brought to the brink of insolvency and merged in 1983, the year the Swatch arrived.

• The Swiss were not behind on the science: at the 1968 Neuchatel Observatory trials, Swiss quartz entries took the first ten places, and the Swiss Beta 21 quartz movement went on show at Basel in 1970.
• Swiss mechanical watch exports fell from about 40 million in 1973 to about 3 million roughly ten years later.
• By 1997 mechanical watches were only about 10 percent of Swiss output but nearly half its value, the pattern the industry still lives on.

Sources: Swatch Group: Group history (company account of the crisis and merger); Foundation for Economic Education: Markets in time, the rise, fall and revival of Swiss watchmaking; Gear Patrol: The Seiko quartz watch that broke Switzerland; Wikipedia: Quartz crisis

UTC and the leap second (1972 to 2027) (1 January 1972)

Coordinated Universal Time took effect on 1 January 1972. It runs at the rate of atomic clocks, but the Earth's spin wanders, so a leap second was added whenever the gap between the two approached one second. Between 1972 and 2016 there were 27 leap seconds, all positive, and since 2017 UTC has run 37 seconds behind International Atomic Time. In 2022 the General Conference on Weights and Measures decided the allowed gap would be widened by 2035, and on 15 October 2026 it voted that UTC will run continuously from 20 May 2027, letting the gap grow to as much as an hour.

• The leap second of 30 June 2012 tripped up software at Reddit, Mozilla and the airline Qantas, among others.
• A 2025 workshop put the chance of the first ever negative leap second, needed if the Earth kept speeding up, at 30 percent by 2035; none has ever been applied.
• UTC is computed by the International Bureau of Weights and Measures near Paris from atomic clocks in national laboratories around the world, NIST and the US Naval Observatory among them.

Sources: BIPM: Resolution 5 of the 28th CGPM (2026), continuity of UTC; BIPM: Resolution 4 of the 27th CGPM (2022), use and future development of UTC; NIST: A Walk Through Time, world time scales; Euronews: Global timekeeping rules change, leap second scrapped from 2027; Wikipedia: Leap second

Citizen light-powered watches, Crystron to Eco-Drive (1976) (1976 (Eco-Drive from 1995))

Citizen's engineers turned to sunlight during the energy crisis of the early 1970s, built a prototype by 1974 and in 1976 launched the Crystron Solar Cell, which Citizen calls the world's first analogue light-powered watch. Its solar cells on the dial charged a silver-oxide battery. In 1986 amorphous silicon cells that work under indoor light arrived, and by 1995 the power reserve had reached six months, the year Citizen launched its Eco-Drive line. Light passes through the dial to a photocell behind it, which charges a rechargeable cell.

How it was made: The first light-powered Citizen still needed servicing after about five years. Each generation since has stretched how long the watch runs on stored light.

Where it is now: Eco-Drive is now Citizen's core technology, worn in about 140 countries and regions. The Eco-Drive 365 movements of 2023 run for a full year on one charge, even in total darkness.

• The Eco-Drive One of 2016 used a movement just 1 mm thick in a case about 3 mm thick.
• Citizen's Caliber 0100, shown in 2018 and sold in 2019, is rated to within one second a year.
• Charging the first model's silver-oxide battery gave off hydrogen gas, which could swell or leak the battery, so Citizen added a circuit to control the charge.

Try it yourself: A Citizen Eco-Drive: light-powered, no battery changes (Citizen Eco-Drive watch on Amazon)

Sources: Citizen Watch Co.: 50 years of light-powered watches (press release, March 2026); Time+Tide: Citizen Eco-Drive history explained; Europa Star: Citizen and the 50 years of Eco-Drive; Wikipedia: Eco-Drive

Swatch (1983) (1 March 1983)

Swatch was Switzerland's answer to Asian quartz. ETA engineers Elmar Mock and Jacques Müller sketched a quartz watch whose one-piece plastic case doubled as the base of the movement, and Ernst Thomke, head of Ebauches SA, pushed it into automated mass production. It had 51 components and was assembled by machines. Thomke presented it at a press conference on 1 March 1983, priced at 39.90 to 49.90 Swiss francs; the name is short for 'second watch'.

How it began: Mock had been investigating plastic insulators when he and Müller drew the first design. The brand name was registered in July 1982 and a test launch was planned in Texas that autumn; traditional jewellers mostly refused it, so it sold through mass-market shops.

How it ended: Under Nicolas G. Hayek the merged SSIH-ASUAG group became SMH and, in 1998, The Swatch Group, named after the watch. In 2022 Swatch launched the Bioceramic MoonSwatch with Omega.

• About 400,000 Swatches sold in the first half-year, more than 3.5 million in 1984, and the hundred-millionth in 1992.
• The idea of building the movement into the case back came from the 1979 Delirium, an ultra-thin luxury watch.
• Mondaine and Fortis rushed out their own plastic watches, the M-Watch and ID-Watch, in 1983.

Try it yourself: A Swatch Originals plastic quartz watch, still the cheapest way into Swiss-made (Swatch Originals quartz watch on Amazon)

Sources: Europa Star archives: our first look at the Swatch; Swatch Group: Group history; Wikipedia: Swatch

Casio F-91W (1989) (June 1989)

Casio introduced the F-91W in June 1989 to replace the F-87W, aiming a cheap, tough, legible watch at the bottom of the digital market. It was the first design by Ryusuke Moriai, later Casio's chief designer. Its Module 593 quartz movement runs on a single CR2016 lithium cell rated for about seven years, and Casio estimates accuracy at about 30 seconds a month. It weighs 21 grams and has an alarm, an hourly chime, a 1/100-second stopwatch and a small light.

How it was made: Casio wanted to shake up the entry-level digital market, and Moriai's design did it with a resin case, steel back and acrylic lens in a package 8.5 mm thick.

Where it is now: It is still in production at about three million a year, by one estimate. It is only splash-resistant, so it is not a swimming watch.

• Leaked Guantanamo Bay assessment documents called the F-91W 'the sign of al-Qaeda' and cited it against some detainees.
• The Science Museum in London keeps a 1997 F-91W, made in Malaysia, complete with its original packing.
• A WatchGecko writer bought a new one in 2021 for less than 10 pounds.

Try it yourself: The Casio F-91W itself, still in production (Casio F-91W on Amazon)

Sources: Science Museum Group: Digital wrist watch, made by Casio, 1997 (1997-655); WatchGecko: Why I love this 10 pound watch; Wikipedia: Casio F-91W

Radio-controlled 'atomic' clocks and watches (1990) (1990 (signals since 1956))

A radio-controlled clock carries a small receiver that picks up a longwave time code broadcast from a station run by a national time laboratory. In North America that is NIST's WWVB near Fort Collins, Colorado, on 60 kHz; Germany has DCF77 on 77.5 kHz, Britain MSF at Anthorn, and Japan two JJY stations. By 1990 Junghans engineers had fitted a receiver into a digital wristwatch, and the analogue Junghans Mega followed in 1991. Clocks set this way are typically within a hundredth of a second of the standard after each sync.

How it was made: WWVB began broadcasting on 60 kHz in 1956. When NIST raised its power from about 10 kW to 50 kW in 1999, coverage spread across most of North America and cheap radio-controlled clocks and watches took off.

Where it is now: Millions of North Americans now set clocks this way. In 2012 WWVB added a second, phase-modulated time code for newer receivers alongside the old one.

• WWVB's code carries flags for daylight saving time, leap years and leap seconds, which is how these clocks change themselves twice a year.
• NIST's shortwave station WWV has broadcast time signals since 1923, and you can still hear it by phone on (303) 499-7111.
• NIST's guideline is that a radio clock's own movement should drift no more than half a second between syncs.

Try it yourself: An atomic wall clock that sets itself nightly from the WWVB signal (atomic radio controlled wall clock on Amazon)

Sources: NIST: Radio station WWVB; NIST: A Walk Through Time, NIST time services; Wikipedia: Radio clock

Optical lattice clocks (2001) (2001 to today)

In 2001 Hidetoshi Katori of the University of Tokyo proposed trapping neutral atoms in a lattice of laser light tuned to a 'magic' wavelength, so the trap would not disturb the atoms' ticking. His group built the first such clock, with strontium, in 2003. These clocks tick at optical frequencies, far faster than caesium's microwaves, which makes them far more stable. In 2024 a JILA team reported a strontium lattice clock with a systematic uncertainty of 8.1 parts in 10 to the 19th, then the lowest of any clock.

How it was made: Optical clocks come in two families, single trapped ions and neutral atoms in lattices. The lattice approach lets tens of thousands of atoms be measured at once.

Where it is now: They do not yet define the second. In 2026 the CGPM reported that the best optical standards are up to 100 times more accurate than today's caesium realization and asked for a proposal for a new definition at its 2030 meeting.

• At this precision gravity matters: to compare clocks at the 10 to the minus 18 level, their heights must be known to about a centimetre.
• The 2024 record clock held about 40,000 strontium-87 atoms in a vertical lattice and edged out a NIST aluminium-ion clock at 9.4 parts in 10 to the 19th.
• The CGPM noted in 2026 that scientists still had not agreed which atom, or mix of atoms, should define the new second.

Sources: arXiv / Phys. Rev. Lett. 133, 023401 (2024): A clock with 8x10^-19 systematic uncertainty (Aeppli et al.); BIPM: Resolution 4 of the 28th CGPM (2026), on the future definition of the second; Optics & Photonics News: Strontium lattice is now the world's most accurate clock; Physics World: A brief history of timekeeping; Wikipedia: Optical lattice clock

Apple Watch (2015) (24 April 2015)

Apple unveiled the Apple Watch on 9 September 2014 and put it on sale on 24 April 2015, in 38 mm and 42 mm sizes and three collections. Its Digital Crown borrowed the watch winder's knob as a way to scroll and zoom. The first gold Edition models cost 10,000 to 17,000 dollars. By 2019 the research firm Strategy Analytics estimated Apple shipped 30.7 million watches, almost 10 million more than all Swiss watch brands combined.

How it was made: Tim Cook launched it as the most personal product Apple had ever made, a phone companion that told the time, took messages and tracked activity.

Where it is now: It is still Apple's watch line and has grown into a health device. In 2018 it won FDA clearance to take an electrocardiogram.

• Apple briefly stopped selling the Series 9 and Ultra 2 in the US from 21 to 27 December 2023 because of a patent ruling over the blood-oxygen sensor.
• Apple revealed the watch in the 'one more thing' slot of the same September 2014 event that launched the iPhone 6.
• The Series 4 added fall detection that can call emergency services by itself if the wearer does not respond.

Try it yourself: The current Apple Watch Series (Apple Watch Series on Amazon)

Sources: Apple Newsroom: Apple Unveils Apple Watch (9 September 2014); The National: Apple Watch outsells entire Swiss watch industry in 2019; Wikipedia: Apple Watch

The mechanical revival in numbers (2023) (2023 to 2025)

The quartz crisis taught the Swiss to stop competing on accuracy and sell the mechanical watch as a luxury object instead. By 1997 mechanical watches were only about a tenth of Swiss output but nearly half its value. In 2023 Swiss watch exports hit a record 26.7 billion francs. In 2025 they were 25.6 billion francs for only 14.6 million watches, under half the 30.7 million Apple Watches Strategy Analytics estimated Apple shipped in 2019.

• The United States is the biggest market for Swiss watches, taking about 17 percent of exports in 2025.
• In 2025 exports of watches priced above 3,000 francs fell 1.9 percent, while those under 500 francs fell 4.5 percent: the cheap end is shrinking fastest.
• Swiss watch exports to China fell about 12 percent in 2025, and by more than a third over two years.

Try it yourself: Hamilton Khaki Field Mechanical: a hand-wound Swiss field watch at an entry-level price (Hamilton Khaki Field Mechanical on Amazon)

Sources: Swiss federal SME portal (KMU): Watchmaking industry remains under pressure (FH figures); Monochrome Watches: Swiss watch exports in 2025; Foundation for Economic Education: Markets in time, the rise, fall and revival of Swiss watchmaking; The National: Apple Watch outsells entire Swiss watch industry in 2019