Dictionary of Horology



A very hard type of quartz capable of retaining a highly polished surface finish. Resistant to chemical attacks.

Traditionally used to make knife-edge bearings, but also used by the decorative arts to make ornaments such as pins, brooches and other types of jewellery.


Mechanism to automatically release an audible and/or visual signal at a preset time.

ALC 2000

Device manufactured by Witschi Electronic SA for testing water resistance.


Instrument for measuring altitude.

Analog watch

A watch equipped with a dial, hands, and markers and/or numbers to indicate every full hour.

Analog-digital display watch

A watch equipped with an analog display together with a digital liquid crystal display.


Small window carved into the watch dial for displaying indications such as the date, hour, moon phase, etc.

Atmosphere (ATM)

Indicator of water resistance. 5 ATM is roughly equivalent to 50 m, and a watch rated 5 ATM (or 50 m) is designed to be safe under 50 metres of water.

Automatic movement

A watch that has an automatic movement is self-winding. When the wearer is moving his arm, the energy produced is transferred to a rotor that turns and winds the watch’s mainspring.


Chronograph capable of measuring the rate of respiration.

Atomic clock

High precision clock with a resonator consisting of atoms oscillating between two of their energy levels.


Balance spring

A spring attached to the balance wheel in mechanical timepieces. Also known as a hairspring. Helps controlling the speed at which the wheels of a timepiece run.

Band width

The distance between the case lugs.

Bar brooch

Special type of brooch capable of serving as a clasp for suspending a watch.


Instrument for measuring the pressure of the atmosphere.


A grooved ring keeping the crystal of a watch face in place.

Breguet (Abraham-Louis)

Swiss horologist (1747-1823) known for inventing the “tourbillon” mechanism, the “parachute” shock-absorber, the lever escapement with divided impulse-faces, the “Breguet overcoil” balance-spring and a compensation device for watches.


Typically a rectangular device for joining the two ends of a wristlet or strap.

Button battery

A small flat battery used in electronic wristwatches.


Caesium clock

A type of atomic clock based on a certain transition between two energy levels of the ground state of the caesium-133 atom.


In connection with watchmaking caliber or calibre are typically alternative terms for movement.

Cartel clock

Small wall-clock, usually of highly ornamental design, of lozenge or oval shape.


The container encasing the watch movement.

Case diameter

The distance between one end of the watch to the other, not including the crown.

Case thickness

The distance between the highest point of the crystal to the base of the watch case.


The Celsius scale is used for the measurement of temperatures.


Ceramic materials are distinguished by a high mechanical and thermic resistance. In watchmaking it’s primarily used for cases and decorative elements.


A written attestation issued by an official watch rating bureau for watches of the chronometer class.


Element used to plate watch cases to give it a shiny appearance.


Basically a watch with hands showing hours, minutes and seconds, together with stopwatch capabilities.


A precision watch for measuring time accurately in spite of motion or variations in temperature, humidity, and air pressure.


Apparatus for showing the time.


When the surface is hollowed.


When the surface is curving outward.


An electrochemical proces causing deterioration of metal.

Countdown timer

Device permitting countdown of a pre-determined interval of time.


Forgery or imitation.


The button to wind a watch. In a chronograph it may additionally serve as a push-piece.


In watchmaking usually the glass covering the watch dial.


Daily alarm

Alarm that is set to a certain time and sounds every day.

Dasypodius, Conrad (1531-1601)

Swiss mathematician who made the calculations for the second Strasbourg clock.


Alternative term for a date-watch.


Time signal transmitter located in Mainflingen, Germany.


Old term for various small parts of a watch.

Dent, Edward John (1790-1853)

Famous chronometer-maker who experimented with the aim of improving the performance of chronometers.


The face of watches and clocks.

Digital display

A display showing the time in digital form.

Diving watch

Watch designed to withstand immersion to a depth of at least 100 m and to satisfy requirements specified in ISO standard 6425.

Domestic clock

Synonym for ‘clock’.

Dondi, Giacomo (1268-1360)

Italian clockmaker, physician and astronomer. Built an astronomical clock over sixteen years.


Measuring-instrument used by watchmakers, particularly casemakers.

Dual time

A watch capable of showing dual time shows the current local time plus at least one other time zone.


Impervious to dust.

Dutertre, Jean-Baptiste (1715-1742)

French horologist who invented the duplex escapement.


Eight-day clock

A clock that is wound once per week.

Elapsed time

Refers to the amount of time it takes for an object to travel over a specified distance.

Electric buzzer

Vibrating back of watch, activated by a piezo-electric ceramic element.

Ellicott, John (1706-1772)

Clock and watchmaker best known for his work on temperature compensated pendulums and his use of the cylinder escapement.


A device in a watch or clock that measures beats and controls the speed of the going train.


A watchmaker’s magnifying glass.



The part of an analog clock or watch that displays the time.

Flyback hand

A chronograph with a flyback hand can be reset with one push of a button without the need to first stop the chronograph.


A small pocket for carrying a watch. Pocket watches are sometimes known as fob-watches.


Balance used in the earliest clocks.

Fromanteel, Ahasuerus (1607-1693)

Clockmaker of Dutch origin, baptized in Norwich 25 February 1607. The first maker of pendulum clocks in Britain.



Electrolytic proces where a solid surface such as metal is being coated with a thin layer of gold or silver.


The cover protecting the dials of watches or clocks.

Global time

The time of day in time zones all over the world.


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


Ancient instrument for measuring time. The gnomon is a stone obelisk casting a shadow on the ground. Predecessor of the sundial.

Gold-cap case

Gold plated watch case.


Global Positioning System based on a network of satellites transmitting signals to aircrafts, ships, vehicles and other transportation means for determination of position, speed and time.

Graham, George (1673-1751)

Horologist and inventor of the cylinder escapement, the dead-beat clock escapement and the mercurial pendulum.



Aka strike-hammer found in socalled strike clocks. Its primary function is to strike a bell or gong, usually once every full hour.

Hand winding watch

A mechanical watch that needs to be wound regularly by the wearer.

Hatch cover

Trap door in the back of a watch case, generally to give access to a battery.


A low frequency time signal transmitter shut down in 2011 due to cost of needed renovation. The service of HBG is now replaced by the DCF77 time signal.

Hipp, Matthias (1813-1893)

German clockmaker who designed and promoted electric clocks. Also invented electrical looms, traffic signals and pendulum clocks.


The study and measurement of time and the art of making clocks and watches.

The history of horology can be divided into four main periods:

1 – Ancient horology: gnomons, sundials, clepsydras and sandglasses.

2 – Mechanical horology (from ca. 1300): mechanical weight-driven clocks and portable timepieces.

3 – Precision horology (from ca. 1650): This period was dominated by scientists as Galileo, Huygens, Hooke and others. Watches and clocks became more accurate of which the best deviated up to one second per day.

4 – Scientific horology (from ca. 1750): An era in horology particularly marked by the scientists (Phillips, Villarceau, Caspari, C. E. Guillaume, Woog) and the horologists (Berthoud, Pierre Le Roy, Breguet, Janvier, Arnold, Grossmann, Riefler and others).


The art of measuring time.

Huygens, Christiaan (1629-1695)

A Dutch physicist, mathematician, astronomer and inventor of the pendulum clock, the cycloidal pendulum, the balance-spring for watches and more.



Something produced as a copy. In watchmaking typically a cheap production of a watch designed to appear as an original.


Resistant to liquids. Water resistant cases are impervious.


Janvier, Antide (1751-1835)

French clockmaker educated in Latin, Greek, mathematics and astronomy. Known for making ingenious and complicated clocks, including astronomical clocks and clocks showing the tides.

Junghans MEGA 1

The world’s first radio controlled quartz wristwatch synchronized twice a day by the DCF77 transmitter.


Kinetic energy

The energy stored in automatic or manually winding movements. The energy is produced either by the watch wearer’s natural motion of the wrist (automatic watches) or by operating the winding crown (manually winding watches), and then stored in the mainspring.



In watchmaking the term lantern is used about various tools and parts that vaguely resemble certains lanterns.

Lap time

Function in a chronograph or sports watch to measure a period of time from a precise moment has started till the period has finished, aka sequential counting. Some watches has a memory bank to store several lap times.


Liquid Crystal Display.

Lépine, Jean Antoine (1720-1814)

French horologist and inventor of the calibre that bears his name.


A watchmaking dynasty from Winterthur dating back to the end of 15th century. 19 members of this family produced horological pieces. Laurentius I was probably the most prominent of these craftsmen and he produced a very large number of tower clocks of which 16 still exist.


In horology, part or mechanism that disconnects, or interrupts the function of, another part or mechanism.

Light emitting diode

A Light Emitting Diode (LED) is a semiconductor device that emits visible light when an electric current passes through it.

Light reflector

Reflective material placed behind liquid crystal displays to increase contrast.


The extensions on the top and bottom of a wrist watch, where the bracelet, strap or band is attached.

Lutz, Jean Célanis (1800-1863)

Swiss watchmaker, inventor of a special method of hardening steel balance-springs.


Magnetic screen

Component used to protect the whole or a part of a movement from a magnetic field.

Mairet, Sylvain (1805-1890)

Swiss chronometer-maker known for his ingenious work and for the quality of his chronometers.

Manual winding

A watch with a mechanical movement has to be winded manually with the winding crown to keep it running.

Mechanical movement

A mechanical movement is based on the mainspring from which the watch gets its energy. The energy is produced either by the motion of the wrist (automatic mechanical watch), or by winding the crown (manual mechanical watch).


Apparatus for checking water resistance of watches by using high pressure air and measuring a possible leak.


Small generator used in watch movements.

Military time

Based on the full 24 hours of the day rather than 2 segments of 12 hours. Thus 3:00 p.m. equals 15:00 in military time, and 3:00 a.m. equals 3:00 in military time.

Morbier clock

Clock with a long pendulum, usually beating seconds, made at Morbier (Jura).


Electronic watch with a tuning-fork balanced by weights which compensate for the rate variations when the watch is in different positions.

Multi-motor watch

Watch with several motors. This system, mostly used in chronographs, allows independent control of the hands of the different counters.


Nardin, Ulysse (1823-1876)

Famous Swiss builder of marine chronometers.



Apparatus for measuring the moment of inertia of a balance or the elastic torque in a balance spring.


Paillard, Charles Auguste (1840-1895)

Swiss horologist who invented a balance spring made of palladium alloy.


Part of the escapement of a watch or clock.

Passive display

A display requiring external light.


Tint or film that forms on the surface of certain metals in course of time as a result of oxidation.


An ironical term for watches that work badly.

Pellaton, Albert (1832-1914)

Swiss horologist who was noted for his tourbillon chronometers.


Heavy body suspended from a fixed point so that it can swing freely. Used to regulate the mechanism of a clock.

Perpetual calendar

A calendar that automatically adjusts for different lengths of months and leap years.

Perrelet, Abram Louis (1729-1826)

Swiss horologist who invented the perpetual watch and the pedometer.

Philippe, Adrien (1815-1894)

French horologist and founder of the watchmaking company Patek Philippe.

Piguet, Henri Féréol

Swiss watchmaker and inventor of the fly-back chronograph.


Part that turns in a fixed element (bearing) that acts as a support.


Valuable stainless metal used for making watch cases. Soluble in aqua regia.


Synthetic resin used for making watch glasses.

Power reserve

Refers to the amount of time a watch will run after being fully powered or wound.

Power reserve indicator

This feature indicates when a watch needs winding, a new battery or to be recharged.


Button on the side of a watchcase to work a mechanism, as a chronograph.


Quare, Daniel (1649-1724)

English watchmaker who was the first to make a watch with a minute hand.


A mineral also called rock crystal. Rock crystal is used in producing optical glasses and watch glasses due to its transparency.

Quartz watch

Electronic watch with a quartz resonator as its time base.


Radio controlled watch

Also called a radio piloted watch or radio synchronized watch. A watch capable of receiving a time signal from a transmitter connected to an atomic clock and synchronize itself.

Rattrapante chronograph

A chronograph equipped with two second hands that makes it possible to run two measurements simultaneously.


Another term for a sub dial that is typically found within the watch’s main dial.

Reid, Thomas (1746-1831)

Scottish horologist who invented the escapement that bears his name.


A function in a watch that chimes the time when a button is pushed.


Quartz crystals used in quartz watches to produce oscillations of very precise frequency is an example of a resonator.

Rivaz, Pierre-Joseph de (1711-1772)

Watch and clock maker who invented clocks capable of running one year without rewinding.

Rolled gold

A metal base, usually silver or nickel, with a leaf of gold placed upon it and then rolled under heat.


In antique watches, a small dial with a hand, having the same functions as the index of a modern watch.

Rotating bezel

An outer ring graduated into 60 divisions corresponding to 60 minutes. For divers the function is used to determine the amount of remaining oxygen in a standard scuba oxygen tank. All diving watches must be equipped with a rotating bezel.


In automatic mechanical watches, the rotor works to power the watch’s spiral mainspring.

Rubidium clock

Atomic clock that uses a rubidium based resonator.


Sapphire crystal

A popular material in watchmaking due to its extreme resistance to scratches.

Schwilgué, Jean-Baptiste

Horologist and designer of the third astronomical clock of Strasbourg Cathedral.

Screw-down crown

A crown that thread into the watchcase and thus provides great protection to ingress of water.

Second time zone indicator

Second time zone indicator is another name for dual time zone and is basically a secondary dial on a watch that can be set to show a different time zone.

Seconds zero reset

Device for resetting the seconds indication to zero enabling the user to synchronize the seconds exactly with a time signal.

Secular calendar

Device capable of reckoning time in which the beginning, length and divisions of a year is defined, sometimes along with multiyear cycles.

Self-winding watch

A self-winding watch is an automatic mechanically powered watch that is wound by the motion of the wearer’s arm.


Instrument with a graduated arc of 60 degrees and a sighting mechanism used for measuring in degrees, minutes and seconds the height of stars above the horizon, as well as their angular distances.

Shock resistant watch

Specified in ISO 1413 as a watch that will withstand the shock received by falling from a height of 1 m on to a horizontal surface of hard wood.


Chronometric instrument used in aircrafts or ships to indicate Greenwich sidereal time in degrees, minutes and fractions of minutes of arc.

Skeleton caseback

A caseback made of a transparent material.

Solar cell

Component transforming sunlight into electrical energy.

Solar powered

A solar powered watch is equipped with a solar cell allowing the battery to be recharged by sunlight.


Instrument for counting the beats of the heart. In horology, a device capable of measuring the number of heart beats per minute.

Split second

A term referring to a chronograph that has two second hands. While one hand moves continuously, the other one can either be stopped, started or reset to zero.

Split time counter

A device permitting the display of several successive times measured from the same origin.

Spring balance timekeeping instrument

Timekeeping instrument whose time base comprises a spring balance oscillating device.


Not subject to oxidation.

Sterling silver

Silver that is 92.5 percent pure.


A watch capable of measuring durations.

Striking work

In a watch or clock, automatic or hand operated mechanism that strikes the hours.

Sub dial

Small dial, typically attached to the main dial, capable of indicating additional information such as elapsed minutes or the date. Often found in chronographs.

Sully, Henry (1680-1729)

English clockmaker who lived in France for many years. Invented a marine clock for accurate determination of longitude. Founded a watch factory at Versailles in 1718.

Swiss made

A label used to indicate that a wristwatch is made in Switzerland. Also a term used to indicate a high quality watch.

Swiss Watch Chamber of Commerce

Body formed of federations, unions and associations of producers belonging to the Swiss watch industry. Founded in 1876.



Instrument for measuring speed. In watchmaking, a timer or chronograph with a graduated dial on which speed can be read off in kilometres per hour or some other unit.

Tavan, Antoine (1749-1836)

Genevese watchmaker who made precision watches. Known for constructing 12 large-sized models of the principal escapements.


Instrument for measuring distances. In horology, a timer or chronograph with a graduated dial enabling to be read off of the speed of sound through the air at 0 degrees Celsius (333 1/3 metres per second).

Tell-tale clock

A large-sized watch with a push piece making it possible for a watchman to record the times of his rounds or inspections.


Slang word for a watch.

Time base

Part of a watch or clock that determines equal intervals of time like a balance wheel or quartz.

Time counter

Instrument measuring durations.

Time signal

A radio signal transmitted from various longwave radio stations placed in countries all over the world. These transmitters are connected to a very precise atomic clock and the time signals transmitted can be received by radio controlled watches for synchronization.

Time zones

A region of the globe that observes a uniform standard time. Most time zones are offset from Coordinated Universal Time (UTC) by a whole number of hours.

The term is also used for the device which makes it possible to display the time in a single or several time zones, typically defined by country borders.


Highly accurate instrument for measuring and keeping time. Astronomical clocks, quartz clocks and marine chronometers are timekeepers.


A device capable of measuring specific time intervals. There are two main types. The one functions basically as a stopwatch, counting upwards from zero, and the other counts down from a preset time interval.


Element 30 percent stronger and nearly 50 percent lighter than steel and therefore often used in watchmaking. Also very resistant to salt water corrosion.

Tompion, Thomas (1639-1713)

English horologist who was one of the first to construct watches with sprung balances.

Tonneau watch

A tonneau watch has a barrel-shaped watchcase and two convex sides.


A general term that can be used to refer to any counter on a watch.


The gear system of a watch or clock.

Tuning fork

Part with two arms that vibrate at a relatively stable frequency and are used as a resonator in tuning fork watches.



The operation of removing the movement from a watchcase.


Stands for Universal Time Coordinated. Prior to 1972 this time was called Greenwich Mean Time (GMT), but is now referred to as Coordinated Universal Time or Universal Time Coordinated.



Portable timepiece.


Container that protects the watch movement from dust, damp and shocks.

Water resistant watch

A watch designed to prevent water from entering the watchcase during activities such as bathing and swimming.


A term that was formerly used to indicate a water resistant watch, now widely replaced by the term water resistant followed by an indication of water pressure, due to the fact that no watch is 100 percent waterproof.


Part of the train in a watch.


Term used to describe the act of winding a mechanical watch which increases the amount of tension of a spring and thus allow the watch to keep going.

Winding stem

Another name for the crown.

Winnerl, Joseph Thaddeus (1799-1886)

Austrian watchmaker and chronometer maker who invented the first chronoscope, a pocket watch whose second hand could be stopped and restarted independently of the movement.

World time dial

A dial, normally found on the outer edge of a watchface, and printed with the names of cities representing up to 24 time zones all over the world.


Time signal radio station located near Fort Collins in Colorado.



Crystal oscillator that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electric signal with a precise frequency. Used in quartz wristwatches.

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