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# Clock

A clock is an instrument to measure, keep, and indicate time. [1]

## Aaron Lufkin Dennison

Aaron Lufkin Dennison (March 6, 1812 &ndash; January 9, 1895) was an American watchmaker and businessman who founded a number of companies.

## Abbasid Caliphate

The Abbasid Caliphate (or ٱلْخِلافَةُ ٱلْعَبَّاسِيَّة) was the third of the Islamic caliphates to succeed the Islamic prophet Muhammad.

## Abul-Abbas

Abul-Abbas (also Abul Abaz or Abulabaz) was an Asian elephant given to Carolingian emperor Charlemagne by the Abbasid caliph Harun al-Rashid.

Alī Ibn Khalaf al-Murādī, (11th century) was an Andalusi mathematician and astronomer who belonged to the scientific circle of Ṣāʿid al- Andalusī.

## Alarm clock

An alarm clock (or sometimes just an alarm) is a clock that is designed to alert an individual or group of individuals at specified time.

## Alexander Bain (inventor)

Alexander Bain (12 October 1811 – 2 January 1877) was a Scottish inventor and engineer who was first to invent and patent the electric clock.

## Alexander M. Nicholson

Alexander M. Nicholson was an American scientist, most notable for inventing the first crystal oscillator, using a piece of Rochelle salt in 1917 while working at Bell Telephone Laboratories.

## Allan variance

The Allan variance (AVAR), also known as two-sample variance, is a measure of frequency stability in clocks, oscillators and amplifiers, named after David W. Allan and expressed mathematically as \sigma_y^2(\tau).

## Alt.horology

The alt.horology Usenet newsgroup concerns all aspects of horology (the science of time and timekeeping, clocks and watches).

## Alternating current

Alternating current (AC) is an electric current which periodically reverses direction, in contrast to direct current (DC) which flows only in one direction.

## American clock

In the 19th century, many clocks and watches were produced in the United States, especially in Connecticut, where many companies were formed to mass-produce quality timepieces.

## American Institute of Physics

The American Institute of Physics (AIP) promotes science, the profession of physics, publishes physics journals, and produces publications for scientific and engineering societies.

## American Watchmakers-Clockmakers Institute

The American Watchmakers-Clockmakers Institute (AWCI) is a not-for-profit trade association based in the United States that is dedicated to the advancement of the modern watch industry, from which it receives a significant portion of its funding.

## Ammonia

Ammonia is a compound of nitrogen and hydrogen with the formula NH3.

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## Anchor escapement

In horology, the anchor escapement is a type of escapement used in pendulum clocks.

## Ancient Greece

Ancient Greece was a civilization belonging to a period of Greek history from the Greek Dark Ages of the 13th–9th centuries BC to the end of antiquity (AD 600).

## Ancient history

Ancient history is the aggregate of past events, "History" from the beginning of recorded human history and extending as far as the Early Middle Ages or the post-classical history.

## Ancient Rome

In historiography, ancient Rome is Roman civilization from the founding of the city of Rome in the 8th century BC to the collapse of the Western Roman Empire in the 5th century AD, encompassing the Roman Kingdom, Roman Republic and Roman Empire until the fall of the western empire.

## Andronicus of Cyrrhus

Andronicus of Cyrrhus or Andronicus Cyrrhestes (Ἀνδρόνικος Κυρρήστου, Andrónikos Kyrrhēstou), son of Hermias, was a Macedonian astronomer who flourished about 100 BC.

## Arabic Sciences and Philosophy

Arabic Sciences and Philosophy, subtitled A Historical Journal, is a peer-reviewed academic journal published by Cambridge University Press.

## Armillary sphere

An armillary sphere (variations are known as spherical astrolabe, armilla, or armil) is a model of objects in the sky (on the celestial sphere), consisting of a spherical framework of rings, centred on Earth or the Sun, that represent lines of celestial longitude and latitude and other astronomically important features, such as the ecliptic.

## Artuqids

The Artquids or Artuqid dynasty (Modern Turkish: Artuklu Beyliği or Artıklılar, sometimes also spelled as Artukid, Ortoqid or Ortokid; Turkish plural: Artukoğulları; Azeri Turkish: Artıqlı) was a Turkmen dynasty that ruled in Eastern Anatolia, Northern Syria and Northern Iraq in the eleventh and twelfth centuries.

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## Asian elephant

The Asian elephant, or Asiatic elephant (Elephas maximus), is the only living species of the genus Elephas and is distributed in Southeast Asia, from India and Nepal in the west to Borneo in the south.

## Astrolabe

An astrolabe (ἀστρολάβος astrolabos; ٱلأَسْطُرلاب al-Asturlāb; اَختِرِیاب Akhteriab) is an elaborate inclinometer, historically used by astronomers and navigators to measure the inclined position in the sky of a celestial body, day or night.

## Astrology

Astrology is the study of the movements and relative positions of celestial objects as a means for divining information about human affairs and terrestrial events.

## Astron (wristwatch)

The Astron wristwatch, formally known as the Seiko Quartz-Astron 35SQ, was the world's first "quartz clock" wristwatch.

## Astronomical clock

An astronomical clock is a clock with special mechanisms and dials to display astronomical information, such as the relative positions of the sun, moon, zodiacal constellations, and sometimes major planets.

## Asynchronous circuit

An asynchronous circuit, or self-timed circuit, is a sequential digital logic circuit which is not governed by a clock circuit or global clock signal.

## Atom

An atom is the smallest constituent unit of ordinary matter that has the properties of a chemical element.

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## Atomic clock

An atomic clock is a clock device that uses an electron transition frequency in the microwave, optical, or ultraviolet region of the electromagnetic spectrum of atoms as a frequency standard for its timekeeping element.

## Augsburg

Augsburg (Augschburg) is a city in Swabia, Bavaria, Germany.

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## Automaton

An automaton (plural: automata or automatons) is a self-operating machine, or a machine or control mechanism designed to automatically follow a predetermined sequence of operations, or respond to predetermined instructions.

## Automaton clock

An automaton clock or automata clock is a type of striking clock featuring automatons.

## Babylon

Babylon (KA2.DIĜIR.RAKI Bābili(m); Aramaic: בבל, Babel; بَابِل, Bābil; בָּבֶל, Bavel; ܒܒܠ, Bāwēl) was a key kingdom in ancient Mesopotamia from the 18th to 6th centuries BC.

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## Backup battery

A backup battery provides power to a system when the primary source of power is unavailable.

Baghdad (بغداد) is the capital of Iraq.

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## Balance spring

A balance spring, or hairspring, is a spring attached to the balance wheel in mechanical timepieces.

## Balance wheel

A balance wheel, or balance, is the timekeeping device used in mechanical watches and some clocks, analogous to the pendulum in a pendulum clock.

## Balloon clock

A balloon clock is a bracket clock with a waisted or balloon-shaped case.

## Banjo clock

The banjo clock, or banjo timepiece, is an American wall clock with a banjo-shaped case.

## Barrel (horology)

Used in mechanical watches and clocks, a barrel is a cylindrical metal box closed by a cover, with a ring of gear teeth around it, containing a spiral spring called the mainspring, which provides power to run the timepiece.

## Baselworld

Baselworld Watch and Jewellery Show is a trade show of the international watch and jewellery industry, organized each spring in the city of Basel, Switzerland, at Messe Basel.

## BBC

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## Bell

A bell is a directly struck idiophone percussion instrument.

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## Bell Labs

Nokia Bell Labs (formerly named AT&T Bell Laboratories, Bell Telephone Laboratories and Bell Labs) is an American research and scientific development company, owned by Finnish company Nokia.

## Big Ben

Big Ben is the nickname for the Great Bell of the clock at the north end of the Palace of Westminster in London and is usually extended to refer to both the clock and the clock tower.

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## Binary clock

A binary clock is a clock that displays the time of day in a binary format.

## Binary number

In mathematics and digital electronics, a binary number is a number expressed in the base-2 numeral system or binary numeral system, which uses only two symbols: typically 0 (zero) and 1 (one).

## Blois

Blois is a city and the capital of Loir-et-Cher department in central France, situated on the banks of the lower river Loire between Orléans and Tours.

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## Bracket clock

A bracket clock is a style of antique portable table clock made in the 17th and 18th centuries.

## Braille

Braille is a tactile writing system used by people who are visually impaired.

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## British Museum

The British Museum, located in the Bloomsbury area of London, United Kingdom, is a public institution dedicated to human history, art and culture.

## Bulova

Bulova is an American watch brand founded in in 1875 and currently owned by Japanese conglomerate Citizen Watch Co.

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## Bury St Edmunds

Bury St Edmunds is a historic market town and civil parish in the in St Edmundsbury district, in the county of Suffolk, England.

## Byzantium

Byzantium or Byzantion (Ancient Greek: Βυζάντιον, Byzántion) was an ancient Greek colony in early antiquity that later became Constantinople, and later Istanbul.

## Caesium

Caesium (British spelling and IUPAC spelling) or cesium (American spelling) is a chemical element with symbol Cs and atomic number 55.

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## Caesium standard

The caesium standard is a primary frequency standard in which electronic transitions between the two hyperfine ground states of caesium-133 atoms are used to control the output frequency.

## Caliphate

A caliphate (خِلافة) is a state under the leadership of an Islamic steward with the title of caliph (خَليفة), a person considered a religious successor to the Islamic prophet Muhammad and a leader of the entire ummah (community).

## Cambridge University Press

Cambridge University Press (CUP) is the publishing business of the University of Cambridge.

## Candle clock

A candle clock is a thin candle with consistently spaced markings (usually with numbers), that when burned, indicate the passage of periods of time.

## Canonical hours

In the practice of Christianity, canonical hours mark the divisions of the day in terms of periods of fixed prayer at regular intervals.

## Canterbury Cathedral

Canterbury Cathedral in Canterbury, Kent, is one of the oldest and most famous Christian structures in England.

## Cantonese people

The Cantonese people are Han Chinese people originating from or residing in the provinces of Guangdong and Guangxi (together known as Liangguang), in southern mainland China.

## Capacitor

A capacitor is a passive two-terminal electrical component that stores potential energy in an electric field.

## Cape Town

Cape Town (Kaapstad,; Xhosa: iKapa) is a coastal city in South Africa.

## Carriage clock

A carriage clock is a small, spring-driven clock, designed for travelling, developed in the early 19th century in France, where they were also known as "Officers' Clocks".

## Cartel clock

A cartel clock is a cartouche shaped clock designed to hang directly on a wall, very commonly executed in fire-gilt bronze (a.k.a. ormolu).

## Cathode ray tube

The cathode ray tube (CRT) is a vacuum tube that contains one or more electron guns and a phosphorescent screen, and is used to display images.

Celestial navigation, also known as astronavigation, is the ancient and modern practice of position fixing that enables a navigator to transition through a space without having to rely on estimated calculations, or dead reckoning, to know their position.

## Celtic languages

The Celtic languages are a group of related languages descended from Proto-Celtic, or "Common Celtic"; a branch of the greater Indo-European language family.

## Central heating

A central heating system provides warmth to the whole interior of a building (or portion of a building) from one point to multiple rooms.

## Chariot clock

A chariot clock is a type of mantel/table figural clock in the form of a chariot whose dial is set into the wheel or elsewhere, its origins date back to the second half of the 16th century southern Germany.

## Charlemagne

Charlemagne or Charles the Great (Karl der Große, Carlo Magno; 2 April 742 – 28 January 814), numbered Charles I, was King of the Franks from 768, King of the Lombards from 774, and Holy Roman Emperor from 800.

## Chess clock

A chess clock consists of two adjacent clocks with buttons to stop one clock while starting the other, so that the two clocks never run simultaneously.

## China

China, officially the People's Republic of China (PRC), is a unitary one-party sovereign state in East Asia and the world's most populous country, with a population of around /1e9 round 3 billion.

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## Christiaan Huygens

Christiaan Huygens (Hugenius; 14 April 1629 – 8 July 1695) was a Dutch physicist, mathematician, astronomer and inventor, who is widely regarded as one of the greatest scientists of all time and a major figure in the scientific revolution.

## Chronometer watch

A chronometer is a specific type of mechanical timepiece tested and certified to meet certain precision standards.

## Church (building)

A church building or church house, often simply called a church, is a building used for Christian religious activities, particularly for worship services.

A circadian rhythm is any biological process that displays an endogenous, entrainable oscillation of about 24 hours.

## Clock drift

Clock drift refers to several related phenomena where a clock does not run at exactly the same rate as a reference clock.

## Clock face

A clock face, or dial, is the part of an analog clock (or watch) that displays the time through the use of a fixed-numbered dial or dials and moving hands.

## Clock ident

A clock ident is a form of television ident in which a clock is displayed, reading the current time, and usually alongside the logo of that particular television station.

## Clock network

A clock network or clock system is a set of synchronized clocks designed to always show exactly the same time by communicating with each other.

## Clock of the Long Now

The Clock of the Long Now, also called the 10,000-year clock, is a mechanical clock under construction, that is designed to keep time for 10,000 years.

## Clock signal

In electronics and especially synchronous digital circuits, a clock signal is a particular type of signal that oscillates between a high and a low state and is used like a metronome to coordinate actions of digital circuits.

## Clock tower

Clock towers are a specific type of building which houses a turret clock and has one or more clock faces on the upper exterior walls.

## Clockarium

The Clockarium is a museum in Schaerbeek, in the Brussels-Capital Region, Belgium, devoted to the Art Deco ceramic clock.

## Clockkeeper

A clockkeeper, sometimes seen as clock keeper, refers to a form of employment seen prevalently during Middle Age Europe involving the tracking of time and the maintaining of clocks and other timekeeping devices.

## Clockmaker

A clockmaker is an artisan who makes and/or repairs clocks.

## Colgate Clock (Indiana)

The Colgate Clock, located at a former Colgate-Palmolive factory in Clarksville, Indiana, is one of the largest clocks in the world.

## Colgate Clock (Jersey City)

The Colgate Clock is an octagonal clock facing the Hudson River near Exchange Place in Jersey City, New Jersey.

## Computer

A computer is a device that can be instructed to carry out sequences of arithmetic or logical operations automatically via computer programming.

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## Computer monitor

A computer monitor is an output device which displays information in pictorial form.

## Congreve clock

A Congreve clock (also known as Congreve's Rolling Ball Clock or Oscillating Path Rolling Ball Clock) is a type of clock that uses a ball rolling along a zig-zag track rather than a pendulum to regulate the time.

## Conical pendulum

A conical pendulum consists of a weight (or bob) fixed on the end of a string or rod suspended from a pivot.

## Continuous function

In mathematics, a continuous function is a function for which sufficiently small changes in the input result in arbitrarily small changes in the output.

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## Corpus Clock

The Corpus Clock is a large sculptural clock at street level on the outside of the Taylor Library at Corpus Christi College, Cambridge University, in the United Kingdom, at the junction of Bene't Street and Trumpington Street, looking out over King's Parade.

## Cosmo Clock 21

Cosmo Clock 21 is a giant Ferris wheel at the Cosmo World amusement park in the Minato Mirai 21 district of Yokohama, Japan.

## Counter (digital)

In digital logic and computing, a counter is a device which stores (and sometimes displays) the number of times a particular event or process has occurred, often in relationship to a clock signal.

## Counterfeit watch

A counterfeit watch is an illegal copy of an authentic watch.

## Cox's timepiece

Cox's timepiece is a clock developed in the 1760s by James Cox.

## Crystal oscillator

A crystal oscillator is an electronic oscillator circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a precise frequency.

## Cuckoo clock

A cuckoo clock is a typically pendulum-regulated clock that strikes the hours with a sound like a common cuckoo's call and has an automated cuckoo bird that moves with each note.

## Cuckooland Museum

The Cuckooland Museum, previously known as the Cuckoo Clock Museum, is a museum that exhibits mainly cuckoo clocks, located in Tabley, Cheshire, England.

## Daedalus (journal)

Dædalus is a peer-reviewed academic journal founded in 1955 as a replacement for the Proceedings of the American Academy of Arts and Sciences, the volume and numbering system of which it continues.

## Daniel Quare

Daniel Quare (1648 or 1649 – 21 March 1724) was an English clockmaker and instrument maker who Invented a repeating watch movement in 1680 and a portable barometer in 1695.

## Date and time representation by country

Different conventions exist around the world for date and time representation, both written and spoken.

## Day

A day, a unit of time, is approximately the period of time during which the Earth completes one rotation with respect to the Sun (solar day).

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## Debt clock

A debt clock is a public counter, which displays the government debt (also known as public debt or national debt) of a public corporation, usually of a state, and which visualizes the progression through an update every second.

## Decimal time

Decimal time is the representation of the time of day using units which are decimally related.

## Department of Defense master clock

The Department of Defense master clock is the master clock to which time and frequency measurements for the United States Department of Defense are referenced.

## Digital clock

A digital clock is a type of clock that displays the time digitally (i.e. in numerals or other symbols), as opposed to an analog clock, where the time is indicated by the positions of rotating hands.

## Digital data

Digital data, in information theory and information systems, is the discrete, discontinuous representation of information or works.

## Direct current

Direct current (DC) is the unidirectional flow of electric charge.

## Display device

A display device is an output device for presentation of information in visual or tactile form (the latter used for example in tactile electronic displays for blind people).

Doll's head clocks, often known by their French name tête de poupée, were popular during the last quarter of the seventeenth century.

## Donald Hill

Donald Routledge Hill (August 6, 1922 – May 30, 1994)D.

## Doomsday Clock

The Doomsday Clock is a symbol which represents the likelihood of a man-made global catastrophe.

## Dunstable Priory

The Priory Church of St Peter with its monastery (Dunstable Priory) was founded in 1132 by Henry I for Augustinian Canons in Dunstable, Bedfordshire, England.

## Dutch language

The Dutch language is a West Germanic language, spoken by around 23 million people as a first language (including the population of the Netherlands where it is the official language, and about sixty percent of Belgium where it is one of the three official languages) and by another 5 million as a second language.

## Earth

Earth is the third planet from the Sun and the only astronomical object known to harbor life.

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## Earth clock

Earth Clock is a computer program that will display a map of the Earth showing the zones where is day and where is night.

## Edward Barlow (priest)

Edward Barlow, alias Booth (1639–1719), was an English priest and mechanician.

## Egypt

Egypt (مِصر, مَصر, Khēmi), officially the Arab Republic of Egypt, is a transcontinental country spanning the northeast corner of Africa and southwest corner of Asia by a land bridge formed by the Sinai Peninsula.

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## Electric battery

An electric battery is a device consisting of one or more electrochemical cells with external connections provided to power electrical devices such as flashlights, smartphones, and electric cars.

## Electric clock

An electric clock is a clock that is powered by electricity, as opposed to a mechanical clock which is powered by a hanging weight or a mainspring.

## Electric motor

An electric motor is an electrical machine that converts electrical energy into mechanical energy.

## Electrical grid

An electrical grid is an interconnected network for delivering electricity from producers to consumers.

## Electromagnet

An electromagnet is a type of magnet in which the magnetic field is produced by an electric current.

## Electromagnetism

Electromagnetism is a branch of physics involving the study of the electromagnetic force, a type of physical interaction that occurs between electrically charged particles.

## Electron

The electron is a subatomic particle, symbol or, whose electric charge is negative one elementary charge.

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## Electronic oscillator

An electronic oscillator is an electronic circuit that produces a periodic, oscillating electronic signal, often a sine wave or a square wave.

## Electronics

Electronics is the discipline dealing with the development and application of devices and systems involving the flow of electrons in a vacuum, in gaseous media, and in semiconductors.

## Elephant clock

The elephant clock was a medieval invention by Al-Jazari (1136–1206), a Muslim engineer and inventor of various clocks including the Elephant clock which consisted of a weight powered water clock in the form of an Asian elephant.

## Eli Terry

Eli Terry Sr. (April 13, 1772 &ndash; February 24, 1852) was an inventor and clockmaker in Connecticut.

## Energy

In physics, energy is the quantitative property that must be transferred to an object in order to perform work on, or to heat, the object.

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## Energy level

A quantum mechanical system or particle that is bound—that is, confined spatially—can only take on certain discrete values of energy.

## England

England is a country that is part of the United Kingdom.

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## Ephemeris time

The term ephemeris time (often abbreviated ET) can in principle refer to time in connection with any astronomical ephemeris.

## Equation clock

An equation clock is a mechanical clock which includes a mechanism that simulates the equation of time, so that the user can read or calculate solar time, as would be shown by a sundial.

## Equation of time

The equation of time describes the discrepancy between two kinds of solar time.

## Escapement

An escapement is a device in mechanical watches and clocks that transfers energy to the timekeeping element (the "impulse action") and allows the number of its oscillations to be counted (the "locking action").

## Europe

Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere.

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## Federation of the Swiss Watch Industry

The Federation of the Swiss Watch Industry FH, with its headquarters in Bienne, is the Swiss watch industry's leading trade association.

## Feedback

Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause-and-effect that forms a circuit or loop.

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## Flashlight

A flashlight (more often called a torch outside North America) is a portable hand-held electric light.

## Flip clock

A flip clock is an electromechanical, digital time keeping device with the time indicated by numbers that are sequentially revealed by a split-flap display.

## Floral clock

A floral clock, or flower clock, is a large decorative clock with the clock face formed by carpet bedding, usually found in a park or other public recreation area.

## Francis Ronalds

Sir Francis Ronalds FRS (21 February 1788 – 8 August 1873) was an English scientist and inventor, and arguably the first electrical engineer.

## French Empire mantel clock

A French Empire-style mantel clock is a type of elaborately decorated mantel clock made in France during the Napoleonic Empire between 1804–1814/15, although the timekeepers manufactured throughout the Bourbon Restoration (1814/1815–1830) are also included within this art movement since they share subject, decorative elements, shapes and style.

## French Revolution

The French Revolution (Révolution française) was a period of far-reaching social and political upheaval in France and its colonies that lasted from 1789 until 1799.

## Frequency

Frequency is the number of occurrences of a repeating event per unit of time.

## Friction

Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other.

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## Fusee (horology)

Used in antique spring-powered mechanical watches and clocks, a fusee is a cone-shaped pulley with a helical groove around it, wound with a cord or chain which is attached to the mainspring barrel.

## Galileo Galilei

Galileo Galilei (15 February 1564Drake (1978, p. 1). The date of Galileo's birth is given according to the Julian calendar, which was then in force throughout Christendom. In 1582 it was replaced in Italy and several other Catholic countries with the Gregorian calendar. Unless otherwise indicated, dates in this article are given according to the Gregorian calendar. – 8 January 1642) was an Italian polymath.

## Gear

A gear or cogwheel is a rotating machine part having cut like teeth, or cogs, which mesh with another toothed part to transmit torque.

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## Gear train

A gear train is a mechanical system formed by mounting gears on a frame so the teeth of the gears engage.

## Genius

A genius is a person who displays exceptional intellectual ability, creative productivity, universality in genres or originality, typically to a degree that is associated with the achievement of new advances in a domain of knowledge.

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## George Graham (clockmaker)

George Graham (7 July 1673 – 20 November 1751) was an English clockmaker, inventor, and geophysicist, and a Fellow of the Royal Society.

## Germanisches Nationalmuseum

The Germanisches Nationalmuseum is a museum in Nuremberg, Germany.

## Germany

Germany (Deutschland), officially the Federal Republic of Germany (Bundesrepublik Deutschland), is a sovereign state in central-western Europe.

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## Giovanni Dondi dell'Orologio

Giovanni Dondi dell'Orologio (c. 1330 – 1388), also known as Giovanni de' Dondi, was an Italian physician, astronomer and mechanical engineer in Padua, now in Italy.

## Global Positioning System

The Global Positioning System (GPS), originally Navstar GPS, is a satellite-based radionavigation system owned by the United States government and operated by the United States Air Force.

## Gnomon

A gnomon (from Greek γνώμων, gnōmōn, literally: "one that knows or examines") is the part of a sundial that casts a shadow.

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## Grandfather clock

A grandfather clock (also a longcase clock, tall-case clock, or floor clock) is a tall, freestanding, weight-driven pendulum clock with the pendulum held inside the tower or waist of the case.

## Greenwich Mean Time

Greenwich Mean Time (GMT) is the mean solar time at the Royal Observatory in Greenwich, London.

## Guard tour patrol system

A guard tour patrol system is a system for logging the rounds of employees in a variety of situations such as security guards patrolling property, technicians monitoring climate-controlled environments, and correctional officers checking prisoner living areas.

## Harmonic oscillator

In classical mechanics, a harmonic oscillator is a system that, when displaced from its equilibrium position, experiences a restoring force, F, proportional to the displacement, x: where k is a positive constant.

## Harun al-Rashid

Harun al-Rashid (هَارُون الرَشِيد Hārūn Ar-Rašīd; "Harun the Orthodox" or "Harun the Rightly-Guided," 17 March 763 or February 766 — 24 March 809 (148–193 Hijri) was the fifth Abbasid Caliph. His birth date is debated, with various sources giving dates from 763 to 766. His epithet "al-Rashid" translates to "the Orthodox," "the Just," "the Upright," or "the Rightly-Guided." Al-Rashid ruled from 786 to 809, during the peak of the Islamic Golden Age. His time was marked by scientific, cultural, and religious prosperity. Islamic art and music also flourished significantly during his reign. He established the legendary library Bayt al-Hikma ("House of Wisdom") in Baghdad in present-day Iraq, and during his rule Baghdad began to flourish as a center of knowledge, culture and trade. During his rule, the family of Barmakids, which played a deciding role in establishing the Abbasid Caliphate, declined gradually. In 796, he moved his court and government to Raqqa in present-day Syria. A Frankish mission came to offer Harun friendship in 799. Harun sent various presents with the emissaries on their return to Charlemagne's court, including a clock that Charlemagne and his retinue deemed to be a conjuration because of the sounds it emanated and the tricks it displayed every time an hour ticked. The fictional The Book of One Thousand and One Nights is set in Harun's magnificent court and some of its stories involve Harun himself. Harun's life and court have been the subject of many other tales, both factual and fictitious. Some of the Twelver sect of Shia Muslims blame Harun for his supposed role in the murder of their 7th Imam (Musa ibn Ja'far).

## Hertz

The hertz (symbol: Hz) is the derived unit of frequency in the International System of Units (SI) and is defined as one cycle per second.

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## History of science and technology in China

Ancient Chinese scientists and engineers made significant scientific innovations, findings and technological advances across various scientific disciplines including the natural sciences, engineering, medicine, military technology, mathematics, geology and astronomy.

## Homophone

A homophone is a word that is pronounced the same (to varying extent) as another word but differs in meaning.

## Horology

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) is the study of the measurement of time.

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## Hour

An hour (symbol: h; also abbreviated hr.) is a unit of time conventionally reckoned as of a day and scientifically reckoned as 3,599–3,601 seconds, depending on conditions.

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## Hourglass

An hourglass (or sandglass, sand timer, or sand clock) is a device used to measure the passage of time.

## Hydraulics

Hydraulics (from Greek: Υδραυλική) is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids.

## Hydropower

Hydropower or water power (from ύδωρ, "water") is power derived from the energy of falling water or fast running water, which may be harnessed for useful purposes.

## Incense clock

The incense clock is a Chinese timekeeping device that appeared during the Song Dynasty (960-1279) and spread to neighboring East Asian countries such as Japan and Korea.

## India

India (IAST), also called the Republic of India (IAST), is a country in South Asia.

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## Industrial Revolution

The Industrial Revolution was the transition to new manufacturing processes in the period from about 1760 to sometime between 1820 and 1840.

## Integrated circuit

An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, normally silicon.

## Interchangeable parts

Interchangeable parts are parts (components) that are, for practical purposes, identical.

## Internet

The Internet is the global system of interconnected computer networks that use the Internet protocol suite (TCP/IP) to link devices worldwide.

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## Invention

An invention is a unique or novel device, method, composition or process.

## Iron Ring Clock

The Iron Ring Clock is a clock of unusual design created by four Mechanical Engineering students at McMaster University in Hamilton, Ontario, Canada.

## Islam

IslamThere are ten pronunciations of Islam in English, differing in whether the first or second syllable has the stress, whether the s is or, and whether the a is pronounced, or (when the stress is on the first syllable) (Merriam Webster).

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## Ismail al-Jazari

Badīʿ az-Zaman Abū l-ʿIzz ibn Ismāʿīl ibn ar-Razāz al-Jazarī (1136–1206, بديع الزمان أَبُو اَلْعِزِ بْنُ إسْماعِيلِ بْنُ الرِّزاز الجزري) was a Muslim polymath: a scholar, inventor, mechanical engineer, artisan, artist and mathematician.

## Isotopes of caesium

Caesium (55Cs; or cesium) has 40 known isotopes, making it, along with barium and mercury, the element with the most isotopes.

## Jacques Curie

Paul-Jacques Curie (29 October 1855 &ndash; 19 February 1941) was a French physicist and professor of mineralogy at the University of Montpellier.

## Japan

Japan (日本; Nippon or Nihon; formally 日本国 or Nihon-koku, lit. "State of Japan") is a sovereign island country in East Asia.

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## Japanese clock

A is a mechanical clock that has been made to tell traditional Japanese time.

## Jens Olsen's World Clock

Jens Olsen's World Clock or Verdensur is an advanced astronomical clock which is displayed in Copenhagen City Hall.

## Jewel bearing

A jewel bearing is a plain bearing in which a metal spindle turns in a jewel-lined pivot hole.

## Jocelyn de Brakelond

Jocelyn de Brakelond or Jocelin de Brakelonde was an English monk and the author of a chronicle narrating the fortunes of the monastery of Bury St. Edmunds Abbey between 1173 and 1202.

## John Harrison

John Harrison (– 24 March 1776) was a self-educated English carpenter and clockmaker who invented a marine chronometer, a long-sought-after device for solving the problem of calculating longitude while at sea.

## Jost Bürgi

Jost Bürgi (also Joost, Jobst; Latinized surname Burgius or Byrgius; 28 February 1552 &ndash; 31 January 1632), active primarily at the courts in Kassel and Prague, was a Swiss clockmaker, a maker of astronomical instruments and a mathematician.

## Kaifeng

Kaifeng, known previously by several names, is a prefecture-level city in east-central Henan province, China.

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## Kanazawa Station

is a major railway station in Kanazawa, Ishikawa, Japan, operated by West Japan Railway Company (JR West), the private railway operator Hokuriku Railroad, and the third-sector operator IR Ishikawa Railway.

## Kit-Cat Klock

The Kit-Cat Klock is an art deco novelty wall clock shaped like a grinning cat with cartoon eyes that swivel in time with its pendulum tail.

## Ko Wen-je

Ko Wen-je (born 6 August 1959) is a Taiwanese surgeon and politician.

## Korea

Korea is a region in East Asia; since 1945 it has been divided into two distinctive sovereign states: North Korea and South Korea.

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## Lantern clock

A lantern clock is a type of antique weight-driven wall clock, shaped like a lantern.

## Latitude

In geography, latitude is a geographic coordinate that specifies the north–south position of a point on the Earth's surface.

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## Le Défenseur du Temps

Le Défenseur du Temps (The Defender of Time) is a large mechanical work of art in the form of a clock created by the French artist Jacques Monestier.

## Liang Lingzan

Liang Lingzan was a Tang Dynasty military engineer and government official of the Kaiyuan era.

## Light-emitting diode

A light-emitting diode (LED) is a two-lead semiconductor light source.

## Lighthouse clock

A lighthouse clock is a type of mantel clock manufactured in the U. S. from 1818 through 1830s by the American clockmaker Simon Willard, having the dial and works exposed beneath a glass dome on a tapered, cylindrical body.

## Liquid-crystal display

A liquid-crystal display (LCD) is a flat-panel display or other electronically modulated optical device that uses the light-modulating properties of liquid crystals.

## List of clocks

This is a list of clocks that have attained notability because of their historical importance, accuracy, exceptional artistry, architectural value, or size.

## List of international common standards

A list of common and basic information standards, that are related by their frequent and widespread use, and which are conventionally used internationally by industry and organizations.

## List of largest clock faces

This is a list of the largest clock faces in the world.

## List of largest cuckoo clocks

Several unusually large cuckoo clocks have been built and installed in different cities of the world with the aim of attracting visitors, as part of publicity of a cuckoo clock shop, or to serve as a landmark for the community and town.

## Local area network

A local area network (LAN) is a computer network that interconnects computers within a limited area such as a residence, school, laboratory, university campus or office building.

## Local mean time

Local mean time is a form of solar time that corrects the variations of local apparent time, forming a uniform time scale at a specific longitude.

## London Bridge

Several bridges named London Bridge have spanned the River Thames between the City of London and Southwark, in central London.

## Longitude

Longitude, is a geographic coordinate that specifies the east-west position of a point on the Earth's surface.

## Longitude rewards

The longitude rewards were the system of inducement prizes offered by the British government as a simple and practical method for the precise determination of a ship's longitude at sea.

## Louis Essen

Louis Essen FRS O.B.E. (6 September 1908 &ndash; 24 August 1997) was an English physicist whose most notable achievements were in the precise measurement of time and the determination of the speed of light.

## Lunar month

In lunar calendars, a lunar month is the time between two successive syzygies (new moons or full moons).

## Lunar phase

The lunar phase or phase of the Moon is the shape of the directly sunlit portion of the Moon as viewed from Earth.

## Mains electricity

Mains electricity (as it is known in the UK; US terms include grid power, wall power, and domestic power) is the general-purpose alternating-current (AC) electric power supply.

## Mainspring

A mainspring is a spiral torsion spring of metal ribbon—commonly spring steel—used as a power source in mechanical watches, some clocks, and other clockwork mechanisms.

## Mantel clock

Mantel clocks—or shelf clocks—are relatively small house clocks traditionally placed on the shelf, or mantel, above the fireplace.

## Marine chronometer

A marine chronometer is a timepiece that is precise and accurate enough to be used as a portable time standard; it can therefore be used to determine longitude by means of celestial navigation.

Mario Taddei (born September 28, 1972) is an Italian academic, and technical director and chief researcher at the Italian study center Leonardo3 in Milan.

## Maser

A maser (an acronym for "microwave amplification by stimulated emission of radiation") is a device that produces coherent electromagnetic waves through amplification by stimulated emission.

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## Mass production

Mass production, also known as flow production or continuous production, is the production of large amounts of standardized products, including and especially on assembly lines.

## Massachusetts

Massachusetts, officially known as the Commonwealth of Massachusetts, is the most populous state in the New England region of the northeastern United States.

## Master clock

A master clock is a precision clock that provides timing signals to synchronise slave clocks as part of a clock network.

## Mechanical watch

A mechanical watch is a watch that uses a mechanism to measure the passage of time, as opposed to modern quartz watches which function electronically.

## Medieval Latin

Medieval Latin was the form of Latin used in the Middle Ages, primarily as a medium of scholarly exchange, as the liturgical language of Chalcedonian Christianity and the Roman Catholic Church, and as a language of science, literature, law, and administration.

## Mercury (element)

Mercury is a chemical element with symbol Hg and atomic number 80.

## Metric system

The metric system is an internationally adopted decimal system of measurement.

## Metrology

Metrology is the science of measurement.

## Microprocessor

A microprocessor is a computer processor that incorporates the functions of a central processing unit on a single integrated circuit (IC), or at most a few integrated circuits.

## Microwave

Microwaves are a form of electromagnetic radiation with wavelengths ranging from one meter to one millimeter; with frequencies between and.

## Military

A military or armed force is a professional organization formally authorized by a sovereign state to use lethal or deadly force and weapons to support the interests of the state.

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## Minute

The minute is a unit of time or angle.

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## Mobile phone

A mobile phone, known as a cell phone in North America, is a portable telephone that can make and receive calls over a radio frequency link while the user is moving within a telephone service area.

## Modern history

Modern history, the modern period or the modern era, is the linear, global, historiographical approach to the time frame after post-classical history.

## Molecular electronic transition

Molecular electronic transitions take place when electrons in a molecule are excited from one energy level to a higher energy level.The energy change associated with this transition provides information on the structure of a molecule and determines many molecular properties such as color.

## Mora clock

Gustavian Mora clocks are a type of longcase clock which were made in, and derived their name from, the town of Mora in Dalarna province, Sweden.

## Moveable feast

A moveable feast or movable feast is an observance in a Christian liturgical calendar that occurs on a different date (relative to the dominant civil or solar calendar) in different years.

## Movement (clockwork)

In horology, a movement, also known as a caliber, is the mechanism of a clock or watch, as opposed to the case, which encloses and protects the movement, and the face, which displays the time.

## MP3 player

An MP3 player or Digital Audio Player is an electronic device that can play digital audio files.

## Musical clock

A musical clock is a clock that marks the hours of the day with a musical tune played from a spiked cylinder either on bells, organ pipes, bellows, and for quartz clocks, using an electronic sound module.

## Nasreddin

Nasreddin or Nasreddin Hodja was a Seljuq satirical Sufi, born in Hortu Village in Sivrihisar, Eskişehir Province, present-day Turkey and died in 13th century in Akşehir, near Konya, a capital of the Seljuk Sultanate of Rum, in today's Turkey.

## National Association of Watch and Clock Collectors

The National Association of Watch and Clock Collectors (NAWCC) is an American non-profit organization with about 13,000 members.

## National Institute of Standards and Technology

The National Institute of Standards and Technology (NIST) is one of the oldest physical science laboratories in the United States.

## National Physical Laboratory (United Kingdom)

The National Physical Laboratory (NPL) is the national measurement standards laboratory for the United Kingdom, based at Bushy Park in Teddington, London, England.

## Natural language

In neuropsychology, linguistics, and the philosophy of language, a natural language or ordinary language is any language that has evolved naturally in humans through use and repetition without conscious planning or premeditation.

Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.

## Network Time Protocol

Network Time Protocol (NTP) is a networking protocol for clock synchronization between computer systems over packet-switched, variable-latency data networks.

## Nixie tube

A Nixie tube, or cold cathode display, is an electronic device for displaying numerals or other information using glow discharge.

## Noon Gun

The Noon Gun has been a historic time signal in Cape Town, South Africa since 1806.

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## Norwich cathedral astronomical clock

Norwich Cathedral Astronomical Clock was a 14th-century astronomical clock in Norwich Cathedral.

## Nuclear magnetic resonance

Nuclear magnetic resonance (NMR) is a physical phenomenon in which nuclei in a magnetic field absorb and re-emit electromagnetic radiation.

## Numerical digit

A numerical digit is a single symbol (such as "2" or "5") used alone, or in combinations (such as "25"), to represent numbers (such as the number 25) according to some positional numeral systems.

## Nuremberg

Nuremberg (Nürnberg) is a city on the river Pegnitz and on the Rhine–Main–Danube Canal in the German state of Bavaria, in the administrative region of Middle Franconia, about north of Munich.

## Oil-lamp clock

Oil-lamp clocks are clocks consisting of a graduated glass reservoir to hold oil - usually whale oil, which burned cleanly and evenly - supplying the fuel for a built-in lamp.

## Oscillation

Oscillation is the repetitive variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states.

Padua (Padova; Pàdova) is a city and comune in Veneto, northern Italy.

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## Pendulum

A pendulum is a weight suspended from a pivot so that it can swing freely.

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## Pendulum clock

A pendulum clock is a clock that uses a pendulum, a swinging weight, as its timekeeping element.

## Peter Henlein

Peter Henlein (also spelled Henle or Hele) (1485 - August 1542), a locksmith and clockmaker of Nuremberg, Germany, is often considered the inventor of the watch.

## Phase-locked loop

A phase-locked loop or phase lock loop abbreviated as PLL is a control system that generates an output signal whose phase is related to the phase of an input signal.

## Physical Review Letters

Physical Review Letters (PRL), established in 1958, is a peer-reviewed, scientific journal that is published 52 times per year by the American Physical Society.

## Pierre Curie

Pierre Curie (15 May 1859 – 19 April 1906) was a French physicist, a pioneer in crystallography, magnetism, piezoelectricity and radioactivity.

## Piezoelectricity

Piezoelectricity is the electric charge that accumulates in certain solid materials (such as crystals, certain ceramics, and biological matter such as bone, DNA and various proteins) in response to applied mechanical stress.

## Pipe organ clock

A pipe organ clock was a clock that chimed with a small organ pipe built into the unit.

## Pocket watch

A pocket watch (or pocketwatch) is a watch that is made to be carried in a pocket, as opposed to a wristwatch, which is strapped to the wrist.

## Polymath

A polymath (πολυμαθής,, "having learned much,"The term was first recorded in written English in the early seventeenth century Latin: uomo universalis, "universal man") is a person whose expertise spans a significant number of different subject areas—such a person is known to draw on complex bodies of knowledge to solve specific problems.

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## Pope Sylvester II

Pope Sylvester II or Silvester II (– 12 May 1003) was Pope from 2 April 999 to his death in 1003.

## Prime meridian

A prime meridian is a meridian (a line of longitude) in a geographic coordinate system at which longitude is defined to be 0°.

## Projection clock

A projection clock (also called ceiling clock) is an analog or digital clock equipped with a projector that creates an enlarged image of the clock face on any suitable projection screen, most often the ceiling.

## Projector

Acer projector, 2012 A projector or image projector is an optical device that projects an image (or moving images) onto a surface, commonly a projection screen.

## Pulley

A pulley is a wheel on an axle or shaft that is designed to support movement and change of direction of a taut cable or belt, or transfer of power between the shaft and cable or belt.

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## Pulsar clock

A pulsar clock is a clock which depends on counting radio pulses emitted by pulsars.

## Q factor

In physics and engineering the quality factor or Q factor is a dimensionless parameter that describes how underdamped an oscillator or resonator is, and characterizes a resonator's bandwidth relative to its centre frequency.

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## Quantum clock

A quantum clock is a type of atomic clock with laser cooled single ions confined together in an electromagnetic ion trap.

## Quartz

Quartz is a mineral composed of silicon and oxygen atoms in a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical formula of SiO2.

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## Quartz clock

A quartz clock is a clock that uses an electronic oscillator that is regulated by a quartz crystal to keep time.

A radio clock or radio-controlled clock (RCC) is a clock that is automatically synchronized by a time code transmitted by a radio transmitter connected to a time standard such as an atomic clock.

A railroad chronometer or railroad standard watch is a specialized timepiece that once was crucial for safe and correct operation of trains in many countries.

## Real-time clock

A real-time clock (RTC) is a computer clock (most often in the form of an integrated circuit) that keeps track of the current time.

## Remontoire

In mechanical horology, a remontoire (from the French remonter, meaning 'to wind') is a small secondary source of power, a weight or spring, which runs the timekeeping mechanism and is itself periodically rewound by the timepiece's main power source, such as a mainspring.

## Repeater (horology)

A repeater is a complication in a mechanical watch or clock that audibly chimes the hours and often minutes at the press of a button.

## Resonance

In physics, resonance is a phenomenon in which a vibrating system or external force drives another system to oscillate with greater amplitude at specific frequencies.

## Resonator

A resonator is a device or system that exhibits resonance or resonant behavior, that is, it naturally oscillates at some frequencies, called its resonant frequencies, with greater amplitude than at others.

## Revolution in Time

Revolution in Time: Clocks and the Making of the Modern World, is an influential history book by David S. Landes.

## 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.

## Robert Hooke

Robert Hooke FRS (– 3 March 1703) was an English natural philosopher, architect and polymath.

## Rolling ball clock

A rolling ball clock is a clock which displays time by means of balls and rails.

## Romance languages

The Romance languages (also called Romanic languages or Neo-Latin languages) are the modern languages that began evolving from Vulgar Latin between the sixth and ninth centuries and that form a branch of the Italic languages within the Indo-European language family.

## Rood screen

The rood screen (also choir screen, chancel screen, or jube) is a common feature in late medieval church architecture.

## Rota Fortunae

In medieval and ancient philosophy the Wheel of Fortune, or Rota Fortunae, is a symbol of the capricious nature of Fate.

## Rotor (electric)

The rotor is a moving component of an electromagnetic system in the electric motor, electric generator, or alternator.

## Routledge

Routledge is a British multinational publisher.

## Rubik's Clock

Rubik's Clock is a mechanical puzzle invented and patented by Christopher C. Wiggs and Christopher J. Taylor.

## Salisbury cathedral clock

The Salisbury cathedral clock is a large iron-framed clock without a dial located in the aisle of Salisbury Cathedral.

## Sand

Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.

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A satellite navigation or satnav system is a system that uses satellites to provide autonomous geo-spatial positioning.

## Second

The second is the SI base unit of time, commonly understood and historically defined as 1/86,400 of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds each.

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## Seiko

(), commonly known as Seiko, is a Japanese holding company that has subsidiaries which manufactures and sells watches, clocks, electronic devices, semiconductors, jewelries, and optical products.

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## Sens Cathedral

Sens Cathedral (Cathédrale Saint-Étienne de Sens) is a Catholic cathedral in Sens in Burgundy, eastern France.

## Singing bird box

A singing bird box (boîte à oiseau chanteur in French) is a box, usually rectangular-shaped, which contains within a miniature automaton singing bird concealed below an oval lid and activated by means of an operating lever.

## Skeleton clock

A skeleton clock is any clock or wristwatch, though typically mechanical in nature, in which the parts that usually conceal the inner workings of the mechanism have been removed or significantly modified so as to display these inner parts.

## Slave clock

In telecommunication and horology, a slave clock is a clock that depends for its accuracy on another clock, a master clock.

## Solar System

The Solar SystemCapitalization of the name varies.

## Solar time

Solar time is a calculation of the passage of time based on the position of the Sun in the sky.

## Song dynasty

The Song dynasty (960–1279) was an era of Chinese history that began in 960 and continued until 1279.

## Speaking clock

A speaking clock or talking clock is a live or recorded human voice service, usually accessed by telephone, that gives the correct time.

## Speech synthesis

Speech synthesis is the artificial production of human speech.

## Spring (device)

A spring is an elastic object that stores mechanical energy.

## Spring Drive

The Spring Drive is a watch movement that was developed by Seiko Epson through collaboration with Seiko Instruments and Seiko Holdings.

## Sprocket

A sprocket or sprocket-wheel is a profiled wheel with teeth, or cogs, that mesh with a chain, track or other perforated or indented material.

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## St Albans

St Albans is a city in Hertfordshire, England, and the major urban area in the City and District of St Albans.

## Stackfreed

A stackfreed is a simple spring-loaded cam mechanism used in some of the earliest antique spring-driven clocks and watches to even out the force of the mainspring, to improve timekeeping accuracy.

## Standard Chinese

Standard Chinese, also known as Modern Standard Mandarin, Standard Mandarin, or simply Mandarin, is a standard variety of Chinese that is the sole official language of both China and Taiwan (de facto), and also one of the four official languages of Singapore.

## Star clock

A star clock (or nocturnal) is a method of using the stars to determine the time.

## Steam clock

A steam clock is a clock which is fully or partially powered by a steam engine.

## Stepper motor

A stepper motor or step motor or stepping motor is a brushless DC electric motor that divides a full rotation into a number of equal steps.

## Stopwatch

A stopwatch is a handheld timepiece designed to measure the amount of time elapsed from a particular time when it is activated to the time when the piece is deactivated.

## Striking clock

A striking clock (also known as chiming clock) is a clock that sounds the hours audibly on a bell or gong.

## Su Song

Su Song (courtesy name: Zirong 子容) (1020–1101 AD) was a renowned Hokkien polymath who was described as a scientist, mathematician, statesman, astronomer, cartographer, horologist, medical doctor, pharmacologist, mineralogist, zoologist, botanist, mechanical and architectural engineer, poet, antiquarian, and ambassador of the Song Dynasty (960–1279).

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## Sun

The Sun is the star at the center of the Solar System.

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## Sundial

A sundial is a device that tells the time of day when there is sunlight by the apparent position of the Sun in the sky.

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## Susan Kramer, Baroness Kramer

Susan Veronica Kramer, Baroness Kramer, PC (née Richards; born 21 July 1950) is a British Liberal Democrat politician.

## Synchronization

Synchronization is the coordination of events to operate a system in unison.

## Synchronous motor

A synchronous electric motor is an AC motor in which, at steady state, the rotation of the shaft is synchronized with the frequency of the supply current; the rotation period is exactly equal to an integral number of AC cycles.

## System time

In computer science and computer programming, system time represents a computer system's notion of the passing of time.

## Taipei

Taipei, officially known as Taipei City, is the capital and a special municipality of Taiwan (officially known as the Republic of China, "ROC").

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## Talking clock

A talking clock (also called a speaking clock and an auditory clock) is a timekeeping device that presents the time as sounds.

## Tally stick

A tally stick (or simply tally) was an ancient memory aid device used to record and document numbers, quantities, or even messages.

## Technical standard

A technical standard is an established norm or requirement in regard to technical systems.

## The Hague

The Hague (Den Haag,, short for 's-Gravenhage) is a city on the western coast of the Netherlands and the capital of the province of South Holland.

## Thomas Tompion

Thomas Tompion (1639&ndash;1713) was an English clockmaker, watchmaker and mechanician who is still regarded to this day as the Father of English Clockmaking.

## Tide clock

A tide clock is a specially designed clock that keeps track of the Moon's apparent motion around the Earth.

## Time

Time is the indefinite continued progress of existence and events that occur in apparently irreversible succession from the past through the present to the future.

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## Time ball

Time ball or timeball or ball time is an obsolete time-signalling device.

## Time bomb

A time bomb (or a timebomb, time-bomb) is a bomb whose detonation is triggered by a timer.

## Time clock

A time clock, sometimes known as a clock card machine or punch clock or time recorder, is a recording clock used at places of business to record the hours worked by employees.

## Time server

A time server is a server computer that reads the actual time from a reference clock and distributes this information to its clients using a computer network.

## Time signal

A time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day.

## Time zone

A time zone is a region of the globe that observes a uniform standard time for legal, commercial, and social purposes.

## Time-to-digital converter

In electronic instrumentation and signal processing, a time to digital converter (abbreviated TDC) is a device for recognizing events and providing a digital representation of the time they occurred.

## Timeline of time measurement technology

Timeline of time measurement technology.

## Timer

A timer is a specialized type of clock used for measuring specific time intervals.

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## Torsion pendulum clock

A torsion pendulum clock, more commonly known as an anniversary clock or 400-day clock, is a mechanical clock which keeps time with a mechanism called a torsion pendulum.

## Tower of the Winds

The Tower of the Winds or the Horologion of Andronikos Kyrrhestes is an octagonal Pentelic marble clocktower in the Roman Agora in Athens that functioned as a horologion or "timepiece".

## Train station

A train station, railway station, railroad station, or depot (see below) is a railway facility or area where trains regularly stop to load or unload passengers or freight.

## Tuning fork

A tuning fork is an acoustic resonator in the form of a two-pronged fork with the prongs (tines) formed from a U-shaped bar of elastic metal (usually steel).

## Turret clock

A turret clock or a public clock is a clock that is larger than a domestic clock and has a mechanism designed to drive a visual time indicator such as dials and or bells as a public amenity.

## Tycho Brahe

Tycho Brahe (born Tyge Ottesen Brahe;. He adopted the Latinized form "Tycho Brahe" (sometimes written Tÿcho) at around age fifteen. The name Tycho comes from Tyche (Τύχη, meaning "luck" in Greek, Roman equivalent: Fortuna), a tutelary deity of fortune and prosperity of ancient Greek city cults. He is now generally referred to as "Tycho," as was common in Scandinavia in his time, rather than by his surname "Brahe" (a spurious appellative form of his name, Tycho de Brahe, only appears much later). 14 December 154624 October 1601) was a Danish nobleman, astronomer, and writer known for his accurate and comprehensive astronomical and planetary observations.

## United States

The United States of America (USA), commonly known as the United States (U.S.) or America, is a federal republic composed of 50 states, a federal district, five major self-governing territories, and various possessions.

## Vacuum fluorescent display

A vacuum fluorescent display (VFD) is a display device used commonly on consumer electronics equipment such as video cassette recorders, car radios, and microwave ovens.

## Vacuum tube

In electronics, a vacuum tube, an electron tube, or just a tube (North America), or valve (Britain and some other regions) is a device that controls electric current between electrodes in an evacuated container.

## Verge escapement

The verge (or crown wheel) escapement is the earliest known type of mechanical escapement, the mechanism in a mechanical clock that controls its rate by allowing the gear train to advance at regular intervals or 'ticks'.

## Videocassette recorder

A videocassette recorder, VCR, or video recorder is an electromechanical device that records analog audio and analog video from broadcast television or other source on a removable, magnetic tape videocassette, and can play back the recording.

## Visual impairment

Visual impairment, also known as vision impairment or vision loss, is a decreased ability to see to a degree that causes problems not fixable by usual means, such as glasses.

## Vitreous enamel

Vitreous enamel, also called porcelain enamel, is a material made by fusing powdered glass to a substrate by firing, usually between.

Dr.

## Waltham Watch Company

The Waltham Watch Company, also known as the American Waltham Watch Co. and the American Watch Co., produced about 40 million watches, clocks, speedometers, compasses, time fuses, and other precision instruments between 1850 and 1957.

## Watch

A watch is a timepiece intended to be carried or worn by a person.

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## Watchmaker

A watchmaker is an artisan who makes and repairs watches.

## Water clock

A water clock or clepsydra (Greek κλεψύδρα from κλέπτειν kleptein, 'to steal'; ὕδωρ hydor, 'water') is any timepiece in which time is measured by the regulated flow of liquid into (inflow type) or out from (outflow type) a vessel where the amount is then measured.

## Wheel train

In horology, a wheel train (or just train) is the gear train of a mechanical watch or clock.

## William Thomson, 1st Baron Kelvin

William Thomson, 1st Baron Kelvin, (26 June 1824 – 17 December 1907) was a Scots-Irish mathematical physicist and engineer who was born in Belfast in 1824.

## World clock

A world clock is a clock which displays the time for various cities around the world.

## Year

A year is the orbital period of the Earth moving in its orbit around the Sun.

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## Yi Xing

Yi Xing (683–727), born Zhang Sui, was a Chinese astronomer, mathematician, mechanical engineer and Buddhist monk of the Tang dynasty (618&ndash;907).

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## Ytterbium

Ytterbium is a chemical element with symbol Yb and atomic number 70.

## 12-hour clock

The 12-hour clock is a time convention in which the 24 hours of the day are divided into two periods: "The use of AM or PM to designate either noon or midnight can cause ambiguity.

## 24-hour analog dial

Clocks and watches with a 24-hour analog dial have an hour hand that makes one complete revolution, 360°, in a day (24 hours per revolution).

## 24-hour clock

The 24-hour clock is the convention of time keeping in which the day runs from midnight to midnight and is divided into 24 hours, indicated by the hours passed since midnight, from 0 to 23.

## References

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