How every fact on this site was checked
146 facts. Each one is in our own words, each one has a source, and each one was checked against that source on 13 November 2026.
How we check
We read each source and wrote each fact in our own words. Our build stores the text of every source page, and for each fact it checks that the key words and figures, the “checks” in the table, really appear on the source page. If any check fails, the site does not build. Where good sources disagree, we show each version in a “Sources differ” box rather than picking one. Our own worked examples (the pendulum lengths, the gear playground and the pendulum calculator) are labelled as our arithmetic.
Known disagreements
- When Galileo noticed the pendulum. About 1581 (Britannica, clock), c. 1583 with the lamp in Pisa cathedral (Britannica, pendulum), as early as 1582 (NIST).
- Who invented the pendulum clock. Some authorities say Galileo, others Huygens (Britannica); Huygens made the first in 1656, Galileo sketched one but never built it (NIST).
- The anchor escapement. Introduced by English clockmakers with the seconds pendulum in 1670 (Britannica), or built by William Clement in London from 1671 (NIST).
- The first spring-driven clocks. About 1450, probably in southern Germany or northern Italy (Britannica, clock); Peter Henlein of Nuremberg, 1500 to 1510 (NIST); the first watches shortly after 1500 (Britannica, watch).
- The balance spring. Hooke in the late 1650s, not shown to be a spiral, and Huygens probably first with a spiral in 1674–75 (Britannica); Huygens around 1675 (NIST).
- The first mechanical clock. Dunstable Priory, 1283, the oldest known (Britannica); Salisbury Cathedral, 1386, the oldest surviving in England (Britannica); Italian city towers in the first half of the 14th century (NIST).
- Su Song’s tower. 35 ft, 11 m (Britannica) or over 30 feet (NIST).
- Harrison and the prize. Won the 1714 prize (NIST); half the reward recommended in 1765, more tests, and a reward from Parliament in the end (Royal Museums Greenwich).
What we left out
- Popular stories we could not find in a reliable source, such as exact first dates for the escapement, are left out or given as each source words them.
- Prize sums are described in words: the sources give them in old pounds, and their modern values vary.
- Big Ben’s clock gets one fact here; the tower itself is a story for another day.
The log
| # | Fact | Source | Checks |
|---|---|---|---|
| 1 | A clock is a machine that links something moving in equal, regular steps to a counter that adds up the steps. | Encyclopaedia Britannica: Clock | 1 passed |
| 2 | Every clock, 12-hour or 24-hour, works on that same principle. | Encyclopaedia Britannica: Clock | 2 passed |
| 3 | NIST puts it the same way: every clock needs a regular, repeating action to mark off equal bits of time, and a way to count them and show the result. | NIST, A Walk Through Time: Early Clocks | 2 passed |
| 4 | Modern clocks are regulated by a balance wheel, a pendulum, a vibrating crystal or the workings of atoms. | NIST, A Walk Through Time: Early Clocks | 1 passed |
| 5 | The history of timekeeping is the search for ever steadier actions to set a clock’s rate. | NIST, A Walk Through Time: Early Clocks | 1 passed |
| 6 | A gear is a toothed wheel on a turning shaft. | Encyclopaedia Britannica: Gear | 1 passed |
| 7 | Gears work in pairs: the teeth of one mesh with the teeth of the other, passing on turning motion and turning force without slipping. | Encyclopaedia Britannica: Gear | 1 passed |
| 8 | Most gears are round, and round gears keep the speed ratio between their shafts constant. | Encyclopaedia Britannica: Gear | 2 passed |
| 9 | Gears with teeth on non-round shapes make the speed ratio change as they turn. | Encyclopaedia Britannica: Gear | 1 passed |
| 10 | The smaller gear of a pair is called the pinion. | Encyclopaedia Britannica: Gear | 1 passed |
| 11 | If the small pinion drives a bigger gear, the pair slows the motion down and boosts the turning force; drive it the other way and it speeds up but turns more weakly. | Encyclopaedia Britannica: Gear | 2 passed |
| 12 | A driven gear with twice the pinion’s teeth turns with twice the force at half the speed. | Encyclopaedia Britannica: Gear | 3 passed |
| 13 | To run smoothly, gear teeth must be cut to a carefully chosen shape. | Encyclopaedia Britannica: Gear | 1 passed |
| 14 | Gears on parallel shafts can have straight teeth (spur gears) or twisted, screw-like teeth (helical gears). | Encyclopaedia Britannica: Gear | 2 passed |
| 15 | Shafts that meet at an angle use bevel gears, with teeth on cut-off cones. | Encyclopaedia Britannica: Gear | 1 passed |
| 16 | A worm looks like a screw, and its gear like part of a long nut bent round a cylinder. | Encyclopaedia Britannica: Gear | 2 passed |
| 17 | Because a worm is basically a screw it can have just one tooth, which makes a worm and gear good for a big speed change in one step. | Encyclopaedia Britannica: Gear | 2 passed |
| 18 | A spur or helical pinion needs at least five teeth to stay in mesh all the time. | Encyclopaedia Britannica: Gear | 1 passed |
| 19 | For a big ratio between parallel shafts you may need several gear pairs in a row, called a train. | Encyclopaedia Britannica: Gear | 1 passed |
| 20 | The most common angle between shafts that are not parallel is a right angle. | Encyclopaedia Britannica: Gear | 2 passed |
| 21 | In a medieval-style watermill, a series of gears carries the stream’s power from the waterwheel to the millstone. | Encyclopaedia Britannica: Gear | 1 passed |
| 22 | A clock’s wheelwork, or train, is the row of gears that carries motion from the weight or spring, by way of the escapement, to the hands. | Encyclopaedia Britannica: Clock | 1 passed |
| 23 | The wheels and pinions must be made accurately so the power flows as steadily as possible. | Encyclopaedia Britannica: Clock | 1 passed |
| 24 | Power enters through the main, or great, wheel, which turns a pinion, whose rod carries the next wheel, and so on down to the escapement. | Encyclopaedia Britannica: Clock | 2 passed |
| 25 | In clockmakers’ words, a pinion is a gear with few teeth, and an arbor is the turning rod the gears are fixed to. | Encyclopaedia Britannica: Clock | 2 passed |
| 26 | The gear ratios are chosen so that one arbor turns once an hour and can carry the minute hand. | Encyclopaedia Britannica: Clock | 1 passed |
| 27 | A simple 12-to-1 gearing, the motion work, drives the hour hand from the minute hand. | Encyclopaedia Britannica: Clock | 1 passed |
| 28 | A slipping clutch on the minute-hand arbor lets you set the hands. | Encyclopaedia Britannica: Clock | 1 passed |
| 29 | The frame of a simple weight-driven clock is two plates held apart by four pillars. | Encyclopaedia Britannica: Clock | 2 passed |
| 30 | The driving weight hangs from a line wound round a barrel, raised by turning the winding square or by pulling the line. | Encyclopaedia Britannica: Clock | 1 passed |
| 31 | A crutch fixed to the pallet arbor ends in a fork that holds the pendulum rod. | Encyclopaedia Britannica: Clock | 1 passed |
| 32 | The cannon pinion, which drives the hands, turns once an hour. | Encyclopaedia Britannica: Clock | 1 passed |
| 33 | In a modern watch, the gears between barrel and escape wheel step the speed up about 4,000 times, using four pairs of gears. | Encyclopaedia Britannica: Watch | 2 passed |
| 34 | Each pair in a watch usually steps up between 6 and 10 times, with pinions of only 6 to 12 leaves (teeth). | Encyclopaedia Britannica: Watch | 2 passed |
| 35 | An escapement lets motion happen in controlled steps. | Encyclopaedia Britannica: Escapement and Pendulum | 1 passed |
| 36 | In a clock or watch it controls how energy passes from the power source to the counting mechanism. | Encyclopaedia Britannica: Escapement and Pendulum | 1 passed |
| 37 | The real innovation of the weight-driven clock was the escapement, which handed the pull of the falling weight on to the counting gears. | Encyclopaedia Britannica: Clock | 1 passed |
| 38 | The escapement is what makes the tick-tock of a weight-driven clock. | Encyclopaedia Britannica: Clock | 1 passed |
| 39 | The verge escapement, the classic early form that made the mechanical clock possible, was probably invented in 13th-century Europe. | Encyclopaedia Britannica: Escapement and Pendulum | 1 passed |
| 40 | It has a crown-shaped wheel, driven by a weight, whose teeth are stopped in turn by a pair of metal pallets. | Encyclopaedia Britannica: Escapement and Pendulum | 2 passed |
| 41 | The pallets sit on an upright rod, the verge, topped by a crossbar called the foliot with two small weights; moving the weights outwards slows it down. | Encyclopaedia Britannica: Escapement and Pendulum | 2 passed |
| 42 | The verge-and-foliot was the most common escapement. | Encyclopaedia Britannica: Clock | 1 passed |
| 43 | Versions of the verge and foliot ruled for more than 300 years. | NIST, A Walk Through Time: A Revolution in Timekeeping | 1 passed |
| 44 | Their weak point: how fast they swung depended heavily on the driving force and on friction. | NIST, A Walk Through Time: A Revolution in Timekeeping | 1 passed |
| 45 | The anchor escapement, invented in England in the 17th century, works with a pendulum and needs much smaller swings than a verge with a pendulum. | Encyclopaedia Britannica: Escapement and Pendulum | 2 passed |
| 46 | Its pallets are shaped like an upside-down anchor, in the same plane as the wheel. | Encyclopaedia Britannica: Escapement and Pendulum | 1 passed |
| 47 | NIST says William Clement began building clocks with the anchor, or recoil, escapement in London in 1671. | NIST, A Walk Through Time: A Revolution in Timekeeping | 1 passed |
| 48 | Britannica says English clockmakers brought in the long, seconds pendulum with the anchor escapement in 1670. | Encyclopaedia Britannica: Clock | 1 passed |
| 49 | The anchor was a big step up because it disturbs the pendulum less than the verge does. | NIST, A Walk Through Time: A Revolution in Timekeeping | 1 passed |
| 50 | Later escapements were made as detached as possible, giving the swinging part energy while leaving it free to swing. | Encyclopaedia Britannica: Escapement and Pendulum | 1 passed |
| 51 | In a pendulum clock the escape wheel moves on one tooth for each double swing and gives the pendulum a push to keep it going. | Encyclopaedia Britannica: Clock | 1 passed |
| 52 | An ideal escapement would push without getting in the way of the free swing, and push the same every time. | Encyclopaedia Britannica: Clock | 1 passed |
| 53 | Edmund Beckett, later Lord Grimthorpe, invented the double three-legged gravity escapement for the great clock at Westminster, now known as Big Ben, installed in 1859. | Encyclopaedia Britannica: Clock | 3 passed |
| 54 | It became the standard for really accurate tower clocks. | Encyclopaedia Britannica: Clock | 1 passed |
| 55 | Most mechanical watches use the lever escapement, invented in England about 1755 by Thomas Mudge. | Encyclopaedia Britannica: Watch | 1 passed |
| 56 | It leaves the balance free to swing, touching it only to give its push and to be unlocked. | Encyclopaedia Britannica: Watch | 1 passed |
| 57 | The lever is by far the most important watch escapement today. | Encyclopaedia Britannica: Watch | 1 passed |
| 58 | A pendulum is a weight hung from a fixed point so it can swing back and forth under gravity. | Encyclopaedia Britannica: Escapement and Pendulum | 1 passed |
| 59 | Pendulums regulate clocks because each complete swing, the period, takes the same time. | Encyclopaedia Britannica: Escapement and Pendulum | 1 passed |
| 60 | For small swings, the period depends only on the pendulum’s length, and hardly at all on how wide it swings. | Encyclopaedia Britannica: Clock | 1 passed |
| 61 | A heavier bob does not change the period, as long as the length stays the same. | Encyclopaedia Britannica: Escapement and Pendulum | 1 passed |
| 62 | Make a pendulum longer and it swings more slowly. | Encyclopaedia Britannica: Escapement and Pendulum | 1 passed |
| 63 | A pendulum that takes one second per swing is about 39 inches (990 mm) long. | Encyclopaedia Britannica: Clock | 1 passed |
| 64 | Make it just 0.001 inch (0.025 mm) longer and the clock loses about a second a day. | Encyclopaedia Britannica: Clock | 1 passed |
| 65 | Clocks are regulated by raising or lowering the bob on a nut screwed along the rod. | Encyclopaedia Britannica: Clock | 1 passed |
| 66 | A steel-rod pendulum clock loses a second a day for a temperature rise of about 4 °F (2.2 °C). | Encyclopaedia Britannica: Clock | 1 passed |
| 67 | Clockmakers fought this with mercury-jar bobs, gridirons of brass and steel rods, and rods of the special alloy Invar, which barely expands. | Encyclopaedia Britannica: Clock | 3 passed |
| 68 | Gravity is not equally strong everywhere, so the same pendulum swings faster at the poles and at low altitude than at the Equator or up high. | Encyclopaedia Britannica: Escapement and Pendulum | 1 passed |
| 69 | Britannica’s pendulum article says Galileo first noticed the steady period around 1583, comparing a swinging lamp in Pisa cathedral with his pulse. | Encyclopaedia Britannica: Escapement and Pendulum | 1 passed |
| 70 | Britannica’s clock article says about 1581. | Encyclopaedia Britannica: Clock | 1 passed |
| 71 | NIST says Galileo was studying the pendulum as early as 1582, and sketched a pendulum clock but never built one before he died in 1642. | NIST, A Walk Through Time: A Revolution in Timekeeping | 2 passed |
| 72 | Christiaan Huygens made the first pendulum clock in 1656. | NIST, A Walk Through Time: A Revolution in Timekeeping | 1 passed |
| 73 | Some authorities credit Galileo with the pendulum clock and others Huygens. | Encyclopaedia Britannica: Escapement and Pendulum | 1 passed |
| 74 | Huygens made the period truly constant with a pivot that made the bob swing along a curve called a cycloid instead of a circle. | Encyclopaedia Britannica: Escapement and Pendulum | 1 passed |
| 75 | His early pendulum clock was out by less than a minute a day, a first; later versions by less than 10 seconds. | NIST, A Walk Through Time: A Revolution in Timekeeping | 2 passed |
| 76 | Huygens described the pendulum as a clock regulator in his book Horologium (1658), and published Horologium Oscillatorium in 1673. | Encyclopaedia Britannica: Christiaan Huygens | 2 passed |
| 77 | The same Huygens found the true shape of Saturn’s rings and one of its moons. | Encyclopaedia Britannica: Christiaan Huygens | 2 passed |
| 78 | The new eight-day wall clocks had very heavy weights, and many fell off weak plaster walls. | Encyclopaedia Britannica: Clock | 1 passed |
| 79 | So the case was stretched down to the floor, and the grandfather clock was born. | Encyclopaedia Britannica: Clock | 1 passed |
| 80 | In 1721 George Graham got a pendulum clock to within a second a day by correcting for the rod growing and shrinking with temperature. | NIST, A Walk Through Time: A Revolution in Timekeeping | 1 passed |
| 81 | The 1921 Shortt clock had two pendulums: a slave that did the work and gave the free master pendulum its gentle pushes. | NIST, A Walk Through Time: A Revolution in Timekeeping | 2 passed |
| 82 | Siegmund Riefler’s clock of 1889 kept time to a hundredth of a second a day. | NIST, A Walk Through Time: A Revolution in Timekeeping | 1 passed |
| 83 | The mainspring, which drives a watch, is a flat band of spring steel; winding it coils it tighter and stores energy. | Encyclopaedia Britannica: Watch | 2 passed |
| 84 | Britannica says spring-driven clocks first appeared about 1450, probably in southern Germany or northern Italy, the first portable timepieces. | Encyclopaedia Britannica: Clock | 2 passed |
| 85 | NIST credits spring-powered clocks to Peter Henlein of Nuremberg, between 1500 and 1510. | NIST, A Walk Through Time: A Revolution in Timekeeping | 1 passed |
| 86 | Britannica says the first watches appeared shortly after 1500, with early ones made by Henlein, a locksmith in Nürnberg. | Encyclopaedia Britannica: Watch | 1 passed |
| 87 | Early spring clocks ran slower as the mainspring unwound. | NIST, A Walk Through Time: A Revolution in Timekeeping | 1 passed |
| 88 | The dials of the first spring clocks usually had only an hour hand; minute hands were rare until the 1650s. | Encyclopaedia Britannica: Clock | 1 passed |
| 89 | A mainspring pulls harder when fully wound than when nearly run down, a big problem for early watches. | Encyclopaedia Britannica: Watch | 1 passed |
| 90 | The fix was the fusee: a cone-shaped, grooved pulley linked to the spring barrel by gut, later a chain. | Encyclopaedia Britannica: Watch | 2 passed |
| 91 | Fully wound, the chain pulls on the narrow end of the cone; as the spring runs down it pulls on a wider part, so the leverage grows and the force stays almost even. | Encyclopaedia Britannica: Watch | 2 passed |
| 92 | Modern watches use a going barrel instead, which drives the gears directly. | Encyclopaedia Britannica: Watch | 1 passed |
| 93 | Until about 1580 German watch movements were almost all iron; then brass came in. | Encyclopaedia Britannica: Watch | 1 passed |
| 94 | Robert Hooke designed a watch with a balance spring in the late 1650s, but there is no evidence it was a spiral. | Encyclopaedia Britannica: Watch | 1 passed |
| 95 | Britannica says Huygens was probably first to design a watch with a spiral balance spring, in 1674–75. | Encyclopaedia Britannica: Watch | 1 passed |
| 96 | NIST says Huygens developed the balance wheel and spring around 1675, letting watches keep time to 10 minutes a day. | NIST, A Walk Through Time: A Revolution in Timekeeping | 2 passed |
| 97 | The balance spring does for the balance wheel what gravity does for a pendulum: it pulls it back so it swings to and fro. | Encyclopaedia Britannica: Watch | 1 passed |
| 98 | Good watches run their balance pivots in jewels; the first patent for watch jewels was taken out in London in 1704. | Encyclopaedia Britannica: Watch | 2 passed |
| 99 | The first self-winding pocket watch patent was taken out in London in 1780; Louis Recordon’s self-winding wristwatch followed in 1924. | Encyclopaedia Britannica: Watch | 2 passed |
| 100 | Quartz clocks beat pendulums because they have no gears or escapements to upset their steady vibration. | NIST, A Walk Through Time: A Revolution in Timekeeping | 1 passed |
| 101 | One of the oldest water clocks was found in the tomb of the pharaoh Amenhotep I, buried around 1500 BCE. | NIST, A Walk Through Time: Early Clocks | 1 passed |
| 102 | The Greeks called water clocks clepsydras, “water thieves”. | NIST, A Walk Through Time: Early Clocks | 1 passed |
| 103 | The Tower of the Winds in Athens, built in the first century BCE, had a 24-hour water clock. | NIST, A Walk Through Time: Early Clocks | 2 passed |
| 104 | Water flow is very hard to control exactly, so water clocks could never be really accurate. | NIST, A Walk Through Time: Early Clocks | 1 passed |
| 105 | The Antikythera mechanism, an ancient Greek bronze device for showing the movements of the sky, was recovered in 1901 from a shipwreck near the island of Antikythera. | Encyclopaedia Britannica: Antikythera mechanism | 2 passed |
| 106 | It is dated to about 100 BCE, give or take 30 years. | Encyclopaedia Britannica: Antikythera mechanism | 1 passed |
| 107 | X-ray images showed 30 gear wheels inside the fragments. | Encyclopaedia Britannica: Antikythera mechanism | 1 passed |
| 108 | Nothing geared that complicated is known again until medieval cathedral clocks, a thousand years later. | Encyclopaedia Britannica: Antikythera mechanism | 1 passed |
| 109 | It was made of bronze sheet and was probably in a case about the size of a shoebox. | Encyclopaedia Britannica: Antikythera mechanism | 1 passed |
| 110 | A hand-turned shaft is thought to have driven the main gear, one turn for each solar year. | Encyclopaedia Britannica: Antikythera mechanism | 1 passed |
| 111 | Its Moon gearing used epicyclic gears and a pin-in-a-slot to copy the Moon’s uneven speed across the sky. | Encyclopaedia Britannica: Antikythera mechanism | 1 passed |
| 112 | A small dial showed when the Panhellenic games, including the ancient Olympics, were due. | Encyclopaedia Britannica: Antikythera mechanism | 1 passed |
| 113 | Its exact purpose is still unknown. | Encyclopaedia Britannica: Antikythera mechanism | 1 passed |
| 114 | Su Song (1020–1101) built an armillary clock in a tower, powered by a waterwheel and a chain drive. | Encyclopaedia Britannica: Su Song | 2 passed |
| 115 | Britannica gives the tower as 35 feet (11 m) tall. | Encyclopaedia Britannica: Su Song | 1 passed |
| 116 | NIST says it was over 30 feet tall and built in 1088 CE. | NIST, A Walk Through Time: Early Clocks | 2 passed |
| 117 | It used a water-driven escapement invented around 725 CE. | NIST, A Walk Through Time: Early Clocks | 1 passed |
| 118 | Its mechanism used ideas not seen in Europe for hundreds of years. | Encyclopaedia Britannica: Su Song | 1 passed |
| 119 | No one knows where the all-mechanical escapement clock came from; the first may have rung bells calling monks to prayer. | Encyclopaedia Britannica: Clock | 2 passed |
| 120 | The first mechanical clocks clearly recorded were big weight-driven tower (turret) clocks that struck the hours, with no hands or dial. | Encyclopaedia Britannica: Clock | 2 passed |
| 121 | NIST says big mechanical clocks appeared in the towers of Italian cities in the first half of the 14th century. | NIST, A Walk Through Time: A Revolution in Timekeeping | 1 passed |
| 122 | Britannica names the oldest known mechanical clock as one added to Dunstable Priory in Bedfordshire in 1283, which had no face. | Encyclopaedia Britannica: Mainspring and 12-hour clock | 1 passed |
| 123 | The oldest surviving clock in England is at Salisbury Cathedral, from 1386. | Encyclopaedia Britannica: Clock | 1 passed |
| 124 | A clock put up at Rouen in France in 1389 still survives. | Encyclopaedia Britannica: Clock | 1 passed |
| 125 | These early clocks may have been out by as much as half an hour a day. | Encyclopaedia Britannica: Clock | 1 passed |
| 126 | On 22 October 1707 five of Admiral Shovell’s ships struck rocks off the Isles of Scilly, and more than 1400 men died. | Royal Museums Greenwich: What made the search for longitude so important? | 2 passed |
| 127 | Spain set up the first longitude reward scheme, in 1567. | Royal Museums Greenwich: What made the search for longitude so important? | 2 passed |
| 128 | Britain’s Longitude Act became law on 9 July 1714, offering a public reward for finding longitude at sea. | Royal Museums Greenwich: What made the search for longitude so important? | 1 passed |
| 129 | John Harrison was a carpenter who taught himself clockmaking. | Royal Museums Greenwich: Longitude found, the story of Harrison’s timekeepers | 1 passed |
| 130 | His precision longcase clocks of the mid-1720s kept time to a second a month. | Royal Museums Greenwich: Longitude found, the story of Harrison’s timekeepers | 1 passed |
| 131 | He aimed for a portable clock that kept time to within three seconds a day. | Royal Museums Greenwich: Longitude found, the story of Harrison’s timekeepers | 1 passed |
| 132 | He brought his first sea clock, H1, to London in 1735; its two linked swinging balances made it ignore a ship’s motion. | Royal Museums Greenwich: Longitude found, the story of Harrison’s timekeepers | 2 passed |
| 133 | Returning from Lisbon in 1736, Harrison correctly said a headland was the Lizard, not the Start: the ship was 60 miles off course. | Royal Museums Greenwich: Longitude found, the story of Harrison’s timekeepers | 2 passed |
| 134 | He worked on H3 for 19 years. | Royal Museums Greenwich: Longitude found, the story of Harrison’s timekeepers | 1 passed |
| 135 | His clocks correct for temperature and, with clever anti-friction parts, run without any oil. | Royal Museums Greenwich: John Harrison’s marine timekeepers | 1 passed |
| 136 | H4, finished in 1759, is Harrison’s prize-winning longitude watch. | Royal Museums Greenwich collections: H4 | 1 passed |
| 137 | H4 has a 102 mm dial and weighs 1.45 kg. | Royal Museums Greenwich collections: H4 | 2 passed |
| 138 | H4 ticks five times a second: its big balance beats faster and swings wider than a normal watch’s. | Royal Museums Greenwich: Longitude found, the story of Harrison’s timekeepers | 1 passed |
| 139 | On the 1761 trial to Jamaica, William Harrison used H4 to predict landfall at Madeira earlier than the crew expected. | Royal Museums Greenwich: Longitude found, the story of Harrison’s timekeepers | 1 passed |
| 140 | NIST says the chronometer kept time on a rolling ship to about a fifth of a second a day, 10 times better than the prize needed. | NIST, A Walk Through Time: A Revolution in Timekeeping | 2 passed |
| 141 | NIST says that by 1761 it had won the British government’s 1714 prize. | NIST, A Walk Through Time: A Revolution in Timekeeping | 1 passed |
| 142 | Royal Museums Greenwich says the Board recommended only half the reward in 1765, the rest to wait until other makers could build similar timekeepers. | Royal Museums Greenwich: Longitude found, the story of Harrison’s timekeepers | 2 passed |
| 143 | When the Royal Observatory tested H4 for 10 months from 1766, it did not perform well, and the dispute flared again. | Royal Museums Greenwich: Longitude found, the story of Harrison’s timekeepers | 1 passed |
| 144 | Harrison was finally rewarded by Parliament, not by the Board of Longitude, and never got all he felt he was owed. | Royal Museums Greenwich: Longitude found, the story of Harrison’s timekeepers | 2 passed |
| 145 | Marine chronometers were expensive at first, so they spread slowly until simpler, cheaper designs arrived in the early 1800s. | Royal Museums Greenwich: Longitude found, the story of Harrison’s timekeepers | 1 passed |
| 146 | Royal Museums Greenwich displays the original H2, H3 and H4 and a replica of H1 at the Royal Observatory. | Royal Museums Greenwich: Longitude found, the story of Harrison’s timekeepers | 1 passed |