Horological Glossary of Terms
Watch Repair Glossary | Horological Terminology & Watchmaking Definitions
Alarm — A device that makes a sound at a pre-set time. Alarm can be found in both quartz and mechanical watches.
Altimeter — Altimeter measures altitude by responding to changes in barometric pressure. Altimeter watches are mostly used by aviators and climbers.
Analog watch — A watch that consists of hands and a dial with a 12 hour numbers or markers display.
Aperture — A small opening found on dials of certain watches in which certain indicators are provided like the date and hour.
Atomic Time — A time based on the frequency determined by the energy of quantum transitions.
Automatic Watch — Also known as a self-winding watch, is a mechanical watch whose mainspring is wound automatically by the nature of motion on the wearer’s wrist.
Band — Also known as a strap can be made of materials like: leather, rubber, and mesh. Holds the watch on the wearer’s wrist.
Barrel — A cylindrical drum that consists of a gear and teeth. It holds the mainspring of a mechanical watch in its place affecting the power reserve option with its dimensions.
Bezel — A bezel is a ring located on the upper part of the watch body, found outside of the crystal. The purpose of a rotating bezel is to be able to begin timing an event at any given time. The 3 types of bezels are: Fixed bezel which cannot be turned; Uni-directional bezel which is turned in the counter clockwise direction; and Bi- directional turning bezel which can be turned either way.
Bracelet — The bracelet is a flexible metal band that keeps the watch in place on the wearer’s wrist. The Bracelet may be made out of any metal or synthetic material; it is attached to the case with spring bars which are fixed between the lugs with holes. In most bracelets links can be removed at the wearer’s preference.
Bridge — The Bridge is a special shape part fixed very precisely into the main plate. The bridge is made up of holes, posts, pins and jewels. Its function it to keep the different parts in place while allowing them to pivot.
Calendar — A function which indicates days of the month. There are 2 types of displays for indicating the date on a calendar watch: hands, and discs. With hands the day and the month are shown by hands on small dials. With discs the day of the week and names of the months appear on disks which revolve under the dial.
Caliber — A caliber determines a size of the movement. It is based on dimensions used as a unit and terms of reference.
Case — The metal housing that contains the watch’s parts. A watch case is made up of four distinct parts: the bezel, the case band, the case back, and the glass. There are many shapes and materials from which the case may be made.
Carat — Carat is a term used to refer to the measure of weight for gemstones.
Chronograph — A chronograph is an instrument which shows the time as well as measures time. It is a mechanism which is used to measure continuous, or interrupted periods of time.
Chronometer — Refers to a timepiece which fulfills standards and official conditions set by C.O.S.C. in Switzerland.
Clasp — The attachment used to connect the two ends of the watch bracelet around the wrist.
Complication — A complicated timepiece in which several mechanisms have been added to the basic movement. Some of those mechanisms can include, a perpetual calendar, Tourbillion, minute repeater, quarter repeater, or a five-minute repeater.
C.O.S.S — Control Officile Suiss de Chronometers. The official chronometer testing organization in Switzerland.
Crown — The grooved button on the outside of the case, used to set the hands and date on all watches and to wind the mainspring on mechanical watches.
Crystal — Located on the topside of the case covering the dial and hands. The 3 types of crystals are: synthetic, natural, and sapphire crystals. Synthetic crystals are made of soft material and are easily scratched. Natural glass crystal may be scratched by very hard substances. Sapphire crystals can only be damaged by a diamond.
Day/Date Watch — A watch that indicates the date and days of the week.
Deployment Buckle — A clasp that folds under the strap of the watch. The buckle is expanded so that the watch can be slipped and snap shut on the wrist.
Depth Sensor — Instrument found on a diver’s watch that determines the depth, detecting the difference in pressure.
Dial — A flat brass disk known as the watch face that the numerals, indicators, and surface design are applied to.
Digital Display — A display that shows information such as numbers, letters, signs, images, etc. which are provided by electronic signals, and transformed into a visible form in electro-optical display cells.
Diver’s Watch — A watch designed for any underwater activity usually equipped with a rotating bezel, screw down crown, and thicker gaskets (‘O’ rings).
Dual Time Watch — A watch that is capable of measuring current local time as well as at least one other time zone.
Elapsed Time — The actual time it takes an object to travel from a start of a measurement to the last measurement observed.
Engine Turning — Engine Turning or Guilloche refers to delicate engraving designs inscribed onto watch components including: cases, dials, bezels, and movements.
EOL — End-of-Life battery indicator in battery operating watches. Generally the end of battery life is indicated by the sweep second hand ticking once every 4 seconds. When this occurs the battery must be changed immediately.
Escapement — The Escapement is an energy distributing unit. The purpose of the escapement is to maintain and count the oscillations of the balance wheel of a watch, or a pendulum of a clock.
Face — The visible side of the watch, also known as the dial.
Fly-Back Chrono — Fly-back uses an additional hand on a chronograph complication watch to stop independently to measure time interval which can “fly-back” (catch up) with the other hand. Fly-Back chronographs are usually used by pilots and professional athletes.
Function — A term used to describe the different tasks that a watch can perform.
Glass Crystal — Located on the topside of the case, covering and protecting the dial and hands. Natural glass crystal may be scratched by very hard substances.
GMT time zone — Greenwich Mean Time, also known as Zulu Time, and Universal Time Coordinated (UTC). Greenwich, England is the place from where all time zones are measured. It is placed on the Prime Meridian or Zero Longitude, and was set as a standard by which all World Time is set. The World Time was agreed to at the 1884 International Meridian Conference at Washington DC, USA.
Gold — Known as a precious metal, a soft yellow corrosion-resistant element.
Gold Plating — Applying a thin gold layer onto a base metal like silver, or copper to enhance, and give the metal a look of gold. The thickness of gold plating is measured in microns.
Guilloche — Also known as Engine Turning. Referees to delicate engraving designs inscribed onto watch components including: cases, dials, bezels, and movements.
Hands — Serve as indicators on the watch face. Different shapes and appearance of the hands give a watch a certain style. They can be made of brass, steel, gold, or aluminum. The quality of the hands is very important; they must remain firm on their axis if the watch is subjected to a violent shock.
Hairspring — A strip of metal with a rectangular cross-section which is coiled around itself. The hairspring is used in mechanical watches and causes the recoil of the balance wheel.
Hand winding Watch — Also known as a Manual –Winding watch. Operates by manually winding the crown which winds the mainspring and powers the movement. A fully wound mainspring will power the watch for 24 hours, although there are some watches with a 7 day power reserve or longer. It all depends on the quality and price of the watch.
Helium Escape Valve — Found in professional dive watches, used mostly by commercial divers. Commercial Divers often spend prolonged hours in diving bells under great pressure. They often use a breathing medium that consists of helium replacing nitrogen.
Horology — The art of manufacturing or repairing watches and clocks. The science of time measurement.
Jewel — Jewels used in watches are synthetic rubies, they serve as bearings for the gear trains. A pivot which turns in a ruby bearing will encounter a minimum of friction and wear.
Jump Hour indicator — A jump hour indicator takes the place of the hour hand. Instead of the hour hand continuing to move in the circular motion, it is shown by means of numerals in a window on the face of the watch.
Karat — Karat is a measurement of the purity of gold alloys. 24K refers to pure gold, 18K refers to 18 parts of gold mixed with 6 parts of metal.
Kinetic — A kinetic watch has no batteries and does not have to be wound. The watch utilizes the power from the human body that keeps the watch running. The watch is equipped with Oscillating weights that create a magnetic charge and convert it to energy by constant movement of the wearer’s wrist.
Lap Timer — A chronograph function that allows the wearer to measure continuous or interrupted periods of time, for example segments of a race.
LCD Display — Liquid Crystal Display shows time electronically by means of a liquid held in a thin layer between two transparent plates.
Luminous — Luminous paint is a standard feature found on the hands and dials of many modern watches. The purpose of the luminous paint is to help the wear tell time where there is an insufficient amount of light. It gives off visible light through florescence, and it reacts to ultra violet light produced by the sun and florescent light bulbs.
Mainspring — A mainspring is a coiled metal strip with a rectangular cross-section. The energy needed for the watch to work is produced by the uncoiling of the spring, which is wound around the core of the barrel arbor.
Manual Winding Movement — Also known as a hand winding watch. Operates by manually winding the crown which winds the mainspring and powers the movement. A fully wound mainspring will power the watch for 24 hours, although there are some watches with a 7 day power reserve or longer. It all depends on the quality and price of the watch.
Marine Chronometer — A highly accurate mechanical or electronic timekeeper precise enough to be used as a portable time standard used to determine longitude.
Mechanical Movement — A movement powered by a mainspring that runs without the need of an outside electrical source. The movement is composed of multiple parts that allow the mainspring to slowly unwind, releasing energy to move the gears that power the watch.
Micron — A term used in gold plating, referring to the thickness of plating layer applied onto metal.
Military Time / 24:00::00 — A means of representing time sequentially using 24 hours counting from 01:00::00 (12:01am) to 24:00::00 12 midnight.
Military Time / 24:00::00 — A means of representing time sequentially using 24 hours counting from 01:00::00 (12:01am) to 24:00::00 12 midnight.
Minute Repeater — A highly complex mechanism that is activated using a slide or a push-button. The Repeater mechanism sounds a low tone each hour, two tones for each quarter hour.
Moon Phase — An indicator that keeps track of the duration of a lunar cycle. The phases of the moon are shown by a moving disk which bears two images of the moon. One lunar cycle is 29 days, 12 hours, 44 minutes, and 2.8 seconds.
Mother of Pearl — An iridescent milky interior shell of the freshwater mollusk that is used to decorate watch dials. Its color can have a milky white luster, and is also available in an array of colors such as pink, blue, gray, yellow, and more.
Movement — The internal mechanism of a watch. It is the motor that keeps time, and performs all available functions. There are 3 types of movements: Mechanical (Automatic, Manual-Wind), Quartz, and Kinetic. Mechanical movements rely on the mainspring to power the watch. Quartz watches rely on a battery to give the movement power. Kinetic watches are powered by a constant movement of the wrist which allows the oscillating weight to create a magnetic charge and convert it to energy that powers the watch.
O-Ring— O-Ring, also known as a gasket, ensures a water resistant seal between two moving parts, for example: the case back, and the case; and the winding crown and the crown tube. Gaskets can be O rings, flat, or shaped, and can be made out of rubber or plastic.
Perpetual Calendar — A complication indicating day of the week, date, month, and the phases of the moon. In addition, it automatically adjusts for months of varying lengths (28, 29, 30, 31) days.
Platinum — One of the rarest and most durable of precious metals. Because Platinum is wear and tarnish-resistant, it is well suited for making fine jewelry.
Power Reserve — A complication which is designed to show the amount of remaining power the watch has before it stops working. An indicator on the dial shows the amount of remaining autonomy. Modern mechanical watches have a power reserve of 40 hours.
Pulsimeter — A scale on a chronograph watch which is used for measuring pulse rate.
Push- piece — Also known as a Push Button, used to control various functions on a chronograph watch.
Quartz Movement— An electronic watch movement powered by a battery, which uses vibrations of tiny quartz crystals to maintain timing accuracy. Those crystals are made up of silicon and oxygen that crystallize in a hexagonal pattern.
Rattrapante Chronograph — A split second chronograph function. When the chrono mechanism is activated and the split-second push piece is pressed the split- second hand will stop, allowing the user to read the intermediate time, meanwhile the second hand continues to rotate. When the same push piece is pressed again the split second hand will catch up with the chronograph hand.
Retrograde — A watch that displays time in a linear manner instead of showing time in a circular fashion. In other words, the hands are not moving around in a circle; they travel along an arc. When they get to the end, they jump back to the beginning.
Rhodium Plating — A procedure by which a metal surface is coated with a thin layer of Rhodium. The main reasons for plating metal are: to enhance its appearance, and provide protection against corrosion.
Rotating Bezel — A ring located on the upper part of the watch body. The rotating bezel is used either as a tachymeter, or as a countdown timer for sporting or diving events.
Rotor — An Oscillating weight found in automatic watches. Its function is to wind the watch. The rotor is a flat piece of metal usually shaped like a semicircle, which swivels on a pivot with nature of the motion on the wearer’s wrist.
Sapphire Crystal — Located on the topside of the case covering the dial and hands. This is the highest quality transparent crystal, made of synthetic sapphire that is shatter-resistant and scratch- resistant. Sapphire crystals can only be damaged by a diamond.
Screw Down Crown — A Screw-Down crown is an essential feature for any watch intended to use with any water activity. The crown has a gasket that forms a seal with the gasket in the crown tube. The seal is achieved by the matching of a threaded tube on the case with the crowns internal threads which is locked into its place by turning the crown clockwise.
Second Time Zone Indicator — Additional time indicator located on a small dial on the face of the watch, which can be set to the time in another time zone. In other words, it lets the wearer keep track of local time and the time in another country.
Self-winding — Another word for Automatic watch. It is a mechanical watch whose mainspring is wound automatically by the nature of motion on the wearer’s wrist.
Shock Resistant –— The watch’s ability to withstand impact, for instance the dropping of the watch.
Skeleton Watch — A watch in which the case and various parts are of transparent material, thus allowing visibility of the watch’s movement.
Solar Technology Powered — A feature found on quartz battery operating watches. The batteries are recharged via solar panels on the watch dial.
Stainless Steel — An extremely durable metal alloy that is virtually rustproof, and resistant to corrosion and discoloration.
Stepping Motor — A part of a quartz movement that moves the gear train. The stepping motor is made up of three principal parts: the coil, the rotor, and the stator.
Stopwatch / Timer — A handheld timepiece designed to measure intervals of time. Function found on chronograph watches.
Strap — A watchband that holds the watch on the wearer’s wrist. It can be made out of cloth, rubber, or leather and designed into many different sizes and shapes.
Swiss a.o.s.c. — A certificate of origin. A mark identifying a watch that is assembled in Switzerland and has components of Swiss origin.
Tank Watch — A rectangular timepiece created by Louis Cartier. Tank watch is equipped with heavier bars on either side of the watch. This design was inspired by the tank tracks of World War I.
Timer — Instrument used to measure and register intervals of time, without any indication of the time of day.
Titanium — A “Space Age” metal, recognized for its high strength and light weight. Titanium is 30% stronger and nearly 50% lighter than steel. It is resistant to salt water corrosion and discoloration, which makes it a perfect material for Dive watches.
Totaliser — A mechanism that keeps track of and displays elapsed time, often located on a sub dial on the watch face.
Tourbillion — Tourbillion is an additional mechanism of a mechanical watch that counters the effects of gravity, and compensates for the difference in rate caused by different positions. The Tourbillion mechanism is composed of the escapement, balance wheel, hairspring, and the pallet fork. All of those parts are mounted in a rotating cage; the entire assembly rotates around their common axis in order to average out the effects of gravity in different positions. This mechanism is highly complex and is an extremely difficult accomplishment to achieve. Specialized literature must be studied in order to become familiar with the Tourbillion complication.
Uni–directional Rotating Bezel –— A bezel located on the upper part of the watch body, found around the crystal. Uni-Directional bezel is turned in the counter clockwise direction. It is used for timing sport events, and marking elapsed and remaining time while diving.
Water Resistance — A very important feature in modern watches that protects the vital parts against water, dust, and humidity. Different watches can withstand protection against water to certain extents. Please refer to the watch manual, or see the water resistance section for a description of different levels of water resistance.
Winding Crown — The button on the right side of the watchcase, used to wind the mainspring, and set the time and date on the mechanical watches. Used to set the time on quartz watches. Winding crown may be decorated with a cabochon stone, or a decorative cap of a precious metal.
Winding — A tightening of the mainspring in a watch. This can be done manually by turning the crown clockwise or automatically by an oscillating weight (rotor) which is made to swing by the movement of the wearer’s wrist.
World Timer — A Disk on the outer edge of the watch dial which represents 24 different time zones. The World timer can display the current time in any part of the world. The names of the cities are printed on the disk. The hour in a particular time zone can be read by looking at the scale next to the city that the hour hand is pointing to.