Horology ("the study of time", related to Latin horologium from Greek ὡρολόγιον, "instrument for telling the hour", from ὥρα hṓra "hour; time" and -o- interfix and suffix -logy)[1][2] is the study of the measurement of time. Clocks, watches, clockwork, sundials, hourglasses, clepsydras, timers, time recorders, marine chronometers, and atomic clocks are all examples of instruments used to measure time. In current usage, horology refers mainly to the study of mechanical time-keeping devices, while chronometry more broadly includes electronic devices that have largely supplanted mechanical clocks for the best accuracy and precision in time-keeping.

People interested in horology are called horologists. That term is used both by people who deal professionally with timekeeping apparatus (watchmakers, clockmakers), as well as aficionados and scholars of horology. Horology and horologists have numerous organizations, both professional associations and more scholarly societies. The largest horological membership organisation globally is the NAWCC, the National Association of Watch and Clock Collectors, which is USA based, but also has local chapters elsewhere.

Museums and libraries

"Universal Clock" at the Clock Museum in Zacatlán, Puebla, Mexico

There are many horology museums and several specialized libraries devoted to the subject. One example is the Royal Greenwich Observatory, which is also the source of the Prime Meridian (longitude 0° 0' 0"), and the home of the first marine timekeepers accurate enough to determine longitude (made by John Harrison). Other horological museums in the London area include the Clockmakers' Museum, which re-opened at the Science Museum in October 2015, the horological collections at the British Museum, the Science Museum (London), and the Wallace Collection.

One of the more comprehensive museums dedicated to horology is the Musée international d'horlogerie in La Chaux-de-Fonds (Switzerland). The Musée d'Horlogerie du Locle is smaller but located nearby. One of the better horological museums in Germany is the Deutsches Uhrenmuseum in Furtwangen im Schwarzwald, in the Black Forest. The two leading specialised horological museums in North America are the National Watch and Clock Museum in Columbia, Pennsylvania and the American Clock and Watch Museum in Bristol, Connecticut.

The eastern French city of Besançon has the Musée du Temps (Museum of Time) in the historic Palais Grenvelle.

An example of a museum devoted to one particular type of clock is the Cuckooland Museum in the UK, which hosts the world's largest collection of antique cuckoo clocks.

One of the most comprehensive horological libraries open to the public is the National Watch and Clock Library in Columbia, Pennsylvania. Other good horological libraries providing public access are at the Musée international d'horlogerie in Switzerland, at the Deutsches Uhrenmuseum in Germany, and at the Guildhall Library in London.

Another museum dedicated to clocks is the Willard House and Clock Museum in Grafton, Massachusetts.


Notable scholarly horological organizations include:

World exhibitions

  • BaselWorld
  • Geneva Time Exhibition
  • Salon International de la Haute Horlogerie (SIHH)


Term Explanation
Chablon French term for a watch movement (not including the dial and hands), that is not completely assembled.
Ébauche French term (commonly used in English-speaking countries) for a movement blank, i.e., an incomplete watch movement sold as a set of loose parts—comprising the main plate, bridges, train, winding and setting mechanism, and regulator. The timing system, escapement, and mainspring, however, are not parts of the ébauche.
Établissage French term for the method of manufacturing watches or movements by assembling their various components. It generally includes the following operations: receipt, inspection and stocking of the "ébauche", the regulating elements and the other parts of the movement and of the make-up; assembling; springing and timing; fitting the dial and hands; casing; final inspection before packing and dispatching.
Établisseur French term for a watch factory that assembles watches from components it buys from other suppliers.
Factory, works In the Swiss watch industry, the term manufacture is used of a factory that manufacturers watches almost completely, as distinct from an atelier de terminage, which only assembles, times, and fits hands and casing.
Manufacture d'horlogerie French term for a watch factory that produces components (particularly the "ébauche") for its products (watches, alarm and desk clocks, etc.).
Terminage French term denoting the process of assembling watch parts for the account of a producer.
Termineur French term for an independent watchmaker (or workshop) engaged in assembling watches, either wholly or in part, for the account of an "établisseur" or a "manufacture", who supply the necessary loose parts. See "atelier de terminage" above.

See also


  1. ^ "horology". Online Etymology Dictionary.
  2. ^ ὡρολόγιον, ὥρα. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project.

Further reading

Balance spring

A balance spring, or hairspring, is a spring attached to the balance wheel in mechanical timepieces. It causes the balance wheel to oscillate with a resonant frequency when the timepiece is running, which controls the speed at which the wheels of the timepiece turn, thus the rate of movement of the hands. A regulator lever is often fitted, which can be used to alter the free length of the spring and thereby adjust the rate of the timepiece.

The balance spring is a fine spiral or helical torsion spring used in mechanical watches, alarm clocks, kitchen timers, marine chronometers, and other timekeeping mechanisms to control the rate of oscillation of the balance wheel. The balance spring is an essential adjunct to the balance wheel, causing it to oscillate back and forth. The balance spring and balance wheel together form a harmonic oscillator, which oscillates with a precise period or "beat" resisting external disturbances, and is responsible for timekeeping accuracy.

The addition of the balance spring to the balance wheel around 1657 by Robert Hooke and Christiaan Huygens greatly increased the accuracy of portable timepieces, transforming early pocketwatches from expensive novelties to useful timekeepers. Improvements to the balance spring are responsible for further large increases in accuracy since that time. Modern balance springs are made of special low temperature coefficient alloys like nivarox to reduce the effects of temperature changes on the rate, and carefully shaped to minimize the effect of changes in drive force as the mainspring runs down. Before the 1980s, balance wheels and balance springs were used in virtually every portable timekeeping device, but in recent decades electronic quartz timekeeping technology has replaced mechanical clockwork, and the major remaining use of balance springs is in mechanical watches.


Chronometry (from Greek χρόνος chronos, "time" and μέτρον metron, "measure") is the science of the measurement of time, or timekeeping. Chronometry applies to electronic devices, while horology refers to mechanical devices.

It should not to be confused with chronology, the science of locating events in time, which often relies upon it.

Complication (horology)

In horology, a complication refers to any feature in a mechanical timepiece beyond the simple display of hours and minutes. A timepiece indicating only hours and minutes is otherwise known as a simple movement. Common complications in commercial watches are day/date displays, alarms, chronographs (stopwatches), and automatic winding mechanisms.

The more complications in a mechanical watch, the more difficult it is to design, create, assemble, and repair. These stipulations do not apply or refer to quartz watches. A typical date-display chronograph may have up to 250 parts, while a particularly complex watch may have a thousand or more parts. Watches with several complications are referred to as grandes complications.

The initial ultra-complicated watches appeared due to watchmakers' ambitious attempts to unite a great number of functions in a case of a single timepiece. The mechanical clocks with a wide range of functions, including astronomical indications, suggested ideas to the developers of the first pocket watches. As a result, as early as in the 16th century, the horology world witnessed the appearance of numerous complicated and even ultra-complicated watches.

Ultra-complicated watches are produced in strictly limited numbers, with some built as unique instruments. Some watchmaking companies known for making ultra-complicated watches are Breguet, Patek Philippe, and Vacheron Constantin.

Fusee (horology)

Used in antique spring-powered mechanical watches and clocks, a fusee (from the French fusée, wire wound around a spindle) is a cone-shaped pulley with a helical groove around it, wound with a cord or chain which is attached to the mainspring barrel. Fusees were used from the 15th century to the early 20th century to improve timekeeping by equalizing the uneven pull of the mainspring as it ran down. Gawaine Baillie stated of the fusee, "Perhaps no problem in mechanics has ever been solved so simply and so perfectly."

International Museum of Horology

The International Museum of Horology, French: Musée international d'horlogerie, is a horological museum in La Chaux-de-Fonds, Switzerland. It is owned and operated by the city of La Chaux-de-Fonds.

Isochronous timing

A sequence of events is isochronous if the events occur regularly, or at equal time intervals. The term isochronous is used in several technical contexts, but usually refers to the primary subject maintaining a constant period or interval (the reciprocal of frequency), despite variations in other measurable factors in the same system. Isochronous timing is a characteristic of a repeating event whereas synchronous timing refers to the relationship between two or more events.

In dynamical systems theory, an oscillator is called isochronous if its frequency is independent of its amplitude.

In horology, a mechanical clock or watch is isochronous if it runs at the same rate regardless of changes in its drive force, so that it keeps correct time as its mainspring unwinds or chain length varies. Isochrony is important in timekeeping devices.

In electrical power generation, isochronous means that the frequency of the electricity generated is constant under varying load; there is zero generator droop. (See Synchronization (alternating current).)

In telecommunications, an isochronous signal is one where the time interval separating any two corresponding transitions is equal to the unit interval or to a multiple of the unit interval; but phase is arbitrary and potentially varying.

The term is also used in data transmission to describe cases in which corresponding significant instants of two or more sequential signals have a constant phase relationship.

Isochronous burst transmission is used when the information-bearer channel rate is higher than the input data signaling rate.

In the Universal Serial Bus used in computers, isochronous is one of the four data flow types for USB devices (the others being Control, Interrupt and Bulk). It is commonly used for streaming data types such as video or audio sources. Similarly, the IEEE 1394 interface standard, commonly called Firewire, includes support for isochronous streams of audio and video at known constant rates.

In particle accelerators an isochronous cyclotron is a cyclotron where the field strength increases with radius to compensate for relativistic increase in mass with speed.

An isochrone is a contour line of equal time, for instance, in geological layers, tree rings or wave fronts. An isochrone map or diagram shows such contours.

In linguistics, isochrony is the postulated rhythmic division of time into equal portions by a language.

In neurology, isochronic tones are regular beats of a single tone used for brainwave entrainment.

Manufacture d'horlogerie

Manufacture d'horlogerie (meaning "watchmaking manufacturer") is a French language term of horology that has also been adopted in English language as a loanword. In horology, the term is usually encountered in its abbreviated form manufacture. This term is used when describing a wrist watch movement or watchworks fabricator which makes all or most of the parts required for its products in its own production facilities, as opposed to simply assembling watches using parts purchased from other firms.

Movement (clockwork)

In horology, a movement, also known as a caliber, is the mechanism of a watch or timepiece, as opposed to the case, which encloses and protects the movement, and the face, which displays the time. The term originated with mechanical timepieces, whose clockwork movements are made of many moving parts. It is less frequently applied to modern electronic or quartz timepieces, where the word module is often used instead.

In modern mass-produced clocks and watches, the same movement is often inserted into many different styles of case. When buying a quality pocketwatch from the mid-19th to the mid-20th century, for example, the customer would select movement and case individually. Mechanical movements get dirty and the lubricants dry up, so they must periodically be disassembled, cleaned, and lubricated. One source recommends servicing intervals of: 3–5 years for watches, 15–20 years for grandfather clocks, 10–15 years for wall or mantel clocks, 15–20 years for anniversary clocks, and 7 years for cuckoo clocks, with the longer intervals applying to antique timepieces.

Repeater (horology)

A repeater is a complication in a mechanical watch or clock that chimes the hours and often minutes at the press of a button. There are many types of repeater, from the simple repeater which merely strikes the number of hours, to the minute repeater which chimes the time down to the minute, using separate tones for hours, quarter hours, and minutes. They originated before widespread artificial illumination, to allow the time to be determined in the dark, and were also used by the visually impaired. Now they are mostly valued as expensive novelties by watch and clock enthusiasts. Repeaters should not be confused with striking clocks or watches, which do not strike on demand, but merely at regular intervals.

Richard of Wallingford

For the Constable of Wallingford Castle, see Richard of Wallingford.Richard of Wallingford (1292–1336) was an English mathematician, astronomer, horologist, and cleric who made major contributions to astronomy and horology while serving as abbot of St Albans Abbey in Hertfordshire.

Sidereal time

Sidereal time is a timekeeping system that astronomers use to locate celestial objects. Using sidereal time, it is possible to easily point a telescope to the proper coordinates in the night sky. Briefly, sidereal time is a "time scale that is based on Earth's rate of rotation measured relative to the fixed stars".

Viewed from the same location, a star seen at one position in the sky will be seen at the same position on another night at the same sidereal time. This is similar to how the time kept by a sundial can be used to find the location of the Sun. Just as the Sun and Moon appear to rise in the east and set in the west due to the rotation of Earth, so do the stars. Both solar time and sidereal time make use of the regularity of Earth's rotation about its polar axis, solar time following the Sun while sidereal time roughly follows the stars.

More exactly, sidereal time is the angle, measured along the celestial equator, from the observer's meridian to the great circle that passes through the March equinox and both celestial poles, and is usually expressed in hours, minutes, and seconds. Common time on a typical clock measures a slightly longer cycle, accounting not only for Earth's axial rotation but also for Earth's orbit around the Sun.

A sidereal day is approximately 23 hours, 56 minutes, 4.0905 SI seconds (24 hours - 4 minutes + 4 seconds = 86164.0905 s). The March equinox itself precesses slowly westward relative to the fixed stars, completing one revolution in about 26,000 years, so the misnamed sidereal day ("sidereal" is derived from the Latin sidus meaning "star") is 0.0084 seconds shorter than the stellar day, Earth's period of rotation relative to the fixed stars.

The slightly longer "true" sidereal period is measured as the Earth Rotation Angle (ERA), formerly the stellar angle. An increase of 360° in the ERA is a full rotation of the Earth.

Because Earth orbits the Sun once a year, the sidereal time at any given place and time will gain about four minutes against local civil time, every 24 hours, until, after a year has passed, one additional sidereal "day" has elapsed compared to the number of solar days that have gone by.

Time control

A time control is a mechanism in the tournament play of almost all two-player board games so that each round of the match can finish in a timely way and the tournament can proceed. Time controls are typically enforced by means of a game clock, where the times below are given per player. Time pressure (or time trouble or Zeitnot) is the situation of having very little time on a player's clock to complete their remaining moves.

In the case of chess, the World Chess Federation FIDE has a single, classical time control for most of its major events: 90 minutes for the first 40 moves, followed by 30 minutes for the rest of the game, with an addition of 30 seconds per move starting from move one. The Candidates tournament and the World Championship are currently played at 100 minutes for 40 moves, followed by 50 minutes for 20 moves, followed by 15 minutes for the rest of the game, with a 30-second increment starting from move one. Also, FIDE formulates different time controls for fast chess.

Time limit (video gaming)

A time limit is a phrase in video game terminology that is used to make gameplay faster on the threat of losing a life. A typical time limit can range from a single second to multiple minutes.


A timekeeper is an instrument or person that measures the passage of time.


In horology, a tourbillon (; French: [tuʁbijɔ̃] "whirlwind") is an addition to the mechanics of a watch escapement. It was developed around 1795 and patented by the French-Swiss watchmaker Abraham-Louis Breguet on June 26, 1801. In a tourbillon the escapement and balance wheel are mounted in a rotating cage, in order to negate the effects of gravity when the timepiece (thus the escapement) is stuck in a certain position. By continuously rotating the entire balance wheel/escapement assembly at a slow rate (typically about one revolution per minute), the tourbillon averages out positional errors.

Originally an attempt to improve accuracy, tourbillons are still included in some expensive modern watches as a novelty and demonstration of watchmaking virtuosity. The mechanism is usually exposed on the watch's face to show it off.

Wheel train

In horology, a wheel train (or just train) is the gear train of a mechanical watch or clock. Although the term is used for other types of gear trains, the long history of mechanical timepieces has created a traditional terminology for their gear trains which is not used in other applications of gears.

Watch movements are very standardized, and the wheel trains of most watches have the same parts. The wheel trains of clocks are a little more varied, with different numbers of wheels depending on the type of clock and how many hours the clock runs between windings (the "going"). However, the wheel trains of clocks and watches share the same terminology, and are similar enough that they can be described together. The large gears in timepieces are generally called wheels, the smaller gears they mesh with (large to small, large to small) are called pinions, and the shafts that the wheels and pinions are mounted on are called arbors. The wheels are mounted between the plates of the movement, with the pivots rotating in holes in the plates. The pivot holes have semicircular depressions around them, called oil cups, to hold the oil in contact with the shaft by capillary action. There are several wheel trains in a typical clock or watch.

Worshipful Company of Clockmakers

The Worshipful Company of Clockmakers is one of the Livery Companies of the City of London. The Clockmakers were formed by a Royal Charter in 1631. Originally, no person was allowed to sell clocks unless they were a member of the Company. However, such requirements have since been relaxed and later removed. The Company now exists as a charitable institution, as do a majority of Livery Companies.

The Company museum was previously housed in the London Guildhall Library. The collection includes John Harrison's clock H5. Since 2015 the collection has been rehoused in the Science Museum in London. The new display was officially opened by HRH Princess Anne on 22 October 2015.

The Company's archive and library are however still kept at the Guildhall Library.

The Clockmakers' Company ranks sixty-first in the order of precedence for Livery Companies. Its motto is Tempus Rerum Imperator, Latin for Time is the commander of (all) things.


Ébauche (loanword from French, meaning blank, outline or sketch) is a term used in art to denote the first preliminary underpainting or quick sketch in oils for an oil painting. Horology, clockmaking and watchmaking appropriated the term ébauche to refer to an incomplete or unassembled watch movement and its associated components. The French term is regularly used by English-speaking artists and art historians, as well as horologists and hobbyists.

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