Watch Dictionary & Terminology

Alarm	A function on a watch that will make a sound or vibration at a preset time
Altimeter	An altimeter measures altitude, or height above sea level. Recording ascent and descent, an altimeter watch is an important piece of equipment for climbers, walkers, mountaineers and, of course, aviators.
AM/PM Indicator	See Day/Night Indicator
Analog/Digital (Duo) Display aka Anadigi	A watch that displays the time, both by hour and minute hands, (an analog display) and by digital digits (a digital display). This is also known as duo display or an AnaDigi watch. See Duo Display
Analogue	A watch that uses hands and a dial to tell the time
Annual Calendar	A complication showing the date, day and month at the minimum. Many will also display Moonphase. This watch will correctly adjust for short and long months; however, it will not correctly account for only 28 days of February once in 4 years. See Perpetual Calendar, Moonphase
Aperture	A small opening/window found on the dials of some watches in which certain indications are given, such as the hour and the date
Auto Repeat Countdown Timer	A countdown timer that resets itself as soon as the preset time has elapsed and starts again. The countdown is repeated continuously until the stop button is pushed.
Automatic Winding Movement	An Automatic watch operates with the same principle as a mechanical manual wind watch - with the addition of a weighted pendulum called the "Rotor". The Rotor is attached to the back of the movement, and when the watch is in motion (with regular wear) the rotor spins around the inside of the watch & "automatically" winds the watch, thus eliminating the need to constantly manually wind the watch. It is important to understand that automatic watches also require a manual wind every so often. An automatic watch that has stopped or is at the end of its power reserve due to non-wear should be manually wound 30-40 times. Manually winding an automatic watch after the power reserve has ebbed or the watch has stopped ensures the watch is at full reserve when first worn, so as long as the watch is worn it will remain fully wound. When removed the watch will stay working for the specified amount of time as indicated in your manual (generally 35-45 hours).
Balance Spring	A very fine spring in a mechanical watch that causes the recoil of the balance wheel. The length and adjustment of its length regulates the timekeeping. This is also known as the Hairspring.
Balance Wheel	The part of a mechanical watch movement that oscillates, dividing time into equal segments. This is the regulating mechanism that controls the watch's timekeeping accuracy.
Barrel	A drum that holds the Mainspring in a mechanical watch. The size of the barrel directly affects the length of the Power Reserve. Some watches feature a Double-Barrel which allows for extra long power reserve. The toothed rim of the barrel drives the train.
Bezel	A "Bezel" is a ring on the top side of the case around the crystal. Some (very few) are actually located beneath the crystal. The Bezel's purpose is to measure time increments. Some bezels can be turned in only one direction - uni-direction turning bezels. Other can be turned either way - bi-directional turning bezel. Yet others are fixed & cannot be turned - each has specific uses. The purposes of the rotating Bezel is to be able to begin timing an event at any given time by aligning the bezel's #12 at the beginning point. Fixed Bezel usually features a scale of sorts such as the Tachymeter scale. See Uni-Directional Turning Bezel, Bi-Directional Turning Bezel, Tachymeter Scale
Bi-Directional Rotating Bezel	A bezel that can be moved both clockwise and counter-clockwise. It is used for keeping track of elapsed time. Allowing the bezel to be rotated either way gives maximum flexibility to beginning the timing.
Bracelet	The metal strap that goes around the wearer's wrist. A watch bracelet is typically made up of flexible, separate links that can be removed to adjust the bracelet's length.
Breguet Spring	The spiral hairspring on which the balance swings tends to bunch on opposite sides as it expands or contracts. The constant shift in their gravity disturbs the rate of balance, and Breguet solved the problem in 1795 by upraising the last coil of the spring and giving it a smaller curve. This Breguet overcoil encouraged the spring to develop concentrically, improving the rate of the watch and reducing the wear on the balance pivots.
Bridge	A part that is fixed to the main plate to form the frame of a watch movement. All other parts are mounted inside the frame.
Calendar	A function that indicates day of the month, and sometimes day of the week and the year.
Cambered	This refers to a Domed/Arched Crystal
Caliber or Calibre	Since the early 18th Century, the calibre of a movement has denoted the position and size of its different components, notably the wheel train and the barrel. Today the term is generally used to refer to the movement, its origins or its maker
Case	The metal housing that contains a watch's parts. Stainless steel is most commonly used although titanium, platinum, gold and silver are also common, however increase the price of the watch.
Chronograph	A watch with a stopwatch function. A Chronograph both measures and displays elapsed times in addition to sowing conventional time. Generally the chronograph mechanism is driven by the movement of the watch & operated by two buttons on the edge of the case which start, stop & reset the chronograph. Usually the chronograph seconds hand is the large centre seconds with sub-dials for elapsed minutes & hours - although the exact display may vary. See Split Seconds Chronograph a.k.a. Rattrapantte, Mono (Single) Pusher Chronograph, Fly-Back Chronograph
Chronometer	A precision watch with a movement that has been rated by the official Swiss testing laboratory called the Controle Officiel Suisse des Chronometeres (aka COSC). The standard procedure involves measuring the performance of the movement at 3 different temperatures and in 5 different positions for 15 consecutive days. Mechanical movements that are accurate to -4/+6 seconds per day are awarded a chronometer certificate. Quartz movements must be accurate to +/-0.2 seconds per day, due to the fact that Quartz movements are inherently accurate and do not vary based on position & temperature. Very few brands go through the expense of certifying their Quartz movements. Breitling, for one, does certify their quartz movements - the result is a highly accurate instrument. See Quartz Movement, Mechanical Movement, COSC, click here for a detailed explanation of what to expect from a mechanical wristwatch.
Complication	A watch with functions other than timekeeping. A simple complication would include various chronographs, alarm, annual calendar & GMT functions, to mention a few. A watch with high complications would be called a Grand Complication & would include a perpetual calendar, Tourbillon, minute repeater or equation of time functions, and others. A watch with any additional function is called a complicated watch.
COSC	The official chronometer testing organization in Switzerland COSC "Controle Officiel Suisse des Chronometres". See Chronometer
Countdown Timer	This allows the wearer to know how much of a preset time has passed. Some Quartz versions sound a warning a few seconds before the pre-set time has elapsed.
Crown	The grooved button on the outside of the case, used for setting the hands on a watch, and the day and date, where applicable. It is also used for winding the mainspring of a mechanical watch. The crown is also known as a winder or winding stem. See Screw-Down Crown, Winding Crown
Crystal	This is the clear cover on the watch face (dial). It may be made of glass, plastic, mineral crystal or sapphire crystal (a scratch-resistant synthetic material). Its purpose is to protect the watch face.
Day/Date	A watch that shows both the day of the week and the date of the month.
Day/Night or AM/PM Indicator	A feature that indicates whether the indicated time is AM or PM. This feature can be found mostly (although not limited to) in watches with a GMT/Dual time display or a World Time Display to help know whether it is day or night in the other time zones.
Deployment (Deployant) Buckle	A buckle that attaches to either side of the strap. The buckle is expandable so that the watch can be slipped on the wrist & snaps shut on the wrist. Once set to the correct size it needs not be resized, thus reducing stress to the strap & elongates its life. This buckle also offers additional security while putting on & taking off the watch.
Digital Display	A watch that shows the time in numbers, or digits, rather than hands and a dial. Liquid crystal display (LCD)is commonly used.
Dual Time	A watch that shows local time and the time in at least one other time zone. This is generally displayed by an additional hour hand which tracks time in a 24 hour mode. Some watches have a separate sub-dial showing the full clock at the additional Time Zone. See GMT, World Time Display.
Duo Display	A display that shows the time both by hour and minute hands (an analogue display) and by numbers (a digital display). This is also known as AnaDigi display. See Analog/Digital Display
Dial	This is the face of the watch, showing the time.
Elapsed Time Rotating Bezel	A graduated rotating bezel that is used to keep track of periods of time. The bezel can be rotated so the wearer can align the zero of the bezel with the watch's minutes or seconds hand. The elapsed time can then be read off the bezel, rather than the wearer having to perform a subtraction necessary if he used the watch's regular dial.
EOL	This is the End-Of-Life battery indication in Quartz-powered watches. Generally the seconds begin to tick once in 4 seconds indicating that the power is low and it is time to change the battery.
Engine Turning/Turned	This is a centuries-old craft that, still today, involves the use of antique machines to engrave delicate patterns on metal watch components, including cases, dials, bezels and movements. It is also known as guilloche. See Guilloche
Equation Of Time or EOT	An Equation Of Time (aka EOT) complication indicates the difference between "true" solar time (that of nature) and "mean" solar time (that of man). As the earth orbits around the sun in an elliptical (oval) shape & the axis is tilted - there are only 4 days a year when the day is exactly 24 hours long April 15th, June 14th, September 1st and December 24th. All other days of the year the days are shorter or longer - depending in the position of the earth. This watch will show the difference between the "mean" time & the "true" time. Since the number of the days are fixed year after year (at the same location) a watch can be manufactured to replicate the correction via a shaped cam which elongates & shortens the days accordingly.
Escapement	The device at the heart of virtually all time-keeping mechanisms. It provides the impulses to maintain the oscillations of the balance wheel or pendulum which governs the rate at which the escapement lets the wheels and hands of the watch revolve.
Fly-back Chronograph	Retour-en-vol in French, a chronograph which restarts the instant it is brought back to zero without the need to stop, reset & restart the chronograph - it is particularly useful to pilots. Pressing the lower push-piece only, they can immediately reset the chronograph to time each successive leg of a search pattern. Without this facility they would have to use two push pieces to stop, return to zero and restart the chronograph while starting a new leg.
Function	A term used to describe the various different tasks a watch can perform such as chronograph and countdown timer. These are also known as complications.
Gear Train	The system of gears which transmits power from the mainspring of the watch to the escapement.
GMT Time Zone	Greenwich Mean Time (GMT) is also known as Zulu Time and UTC (Universal Time Coordinated). The standard by which all World Time is set was agreed at the 1884 International Meridian Conference at Washington DC, USA. It placed Greenwich on the Prime Meridian (Zero Longitude). Greenwich Mean Time or GMT is the time standard against which all other time zones in the world are referenced. It is the same all year round and is not affected by Summer Time or Daylight Savings Time. GMT was originally set-up to aid naval navigation when the globe started to open up with the discovery of the "New World" (America) in the fifteenth Century. Generally when the GMT term is used with watches it refers to the ability of the watch that shows local time and the time in at least one other time zone in a 24 hour mode. The reason for showing the additional time zone in 24 hour mode is to allow the wearer to know if the second time zone is in AM or PM. See Dual Time, World Time
Gold Plating	A layer of gold that is plated onto a base metal case or bracelet to enhance its looks. The thickness of the plating is measured in microns (1000th of a mm).
Guilloche	Guilloche a.k.a. Engine Turning is an engraving technique in which a very precise intricate repetitive patterns or design is mechanically etched into an underlying material with very fine detail. Specifically, it involves a technique of engine turning, called guilloche in French, after the French engineer "Guillot", who invented a machine that could scratch fine patterns and designs on metallic surfaces. See Engine Turning
Hairspring	A very fine spring in a mechanical watch that causes the recoil of the balance wheel. The length and adjustment of its length regulate the watch's timekeeping. It is also known as a balance spring.
Helium Escape Valve	Professional Divers watches are designed with the needs of deep water divers in mind. These divers regularly spend extended periods of time in diving bells at pressure, breathing Hypoxic trimix or other mixed gases with helium in them. Because helium is such a small molecule (the second smallest there is), over time in a pressurized diving bell, helium will sneak its way past the o-rings into the inside of a dive watch. While at depth this causes no problem, it will as the divers decompress the helium which is unable to escape the watch. With a standard dive watch this would lead to the watch crystal popping out from internal pressure. To stop this happening, high-end, professional diver watches have a helium escape valve or helium bleed valve to let out this extra pressure during decompression. This is a one-way valve which allows the helium to escape.
Horology	The science of time measurement, encompassing the art of designing and constructing watches.
Index Hour Marker	A simple stick/line design hour indicator on an analog watch dial, used instead of numerals.
Jewels	Synthetic gemstones that act as bearings for the gear trains, reducing friction and wear.
Jump Hour/Minutes	Instead of a hand continuing to move, a "jumping display" uses numerals seen through an aperture, which instantly change on the hour (or minute). The circular motion of hands has been adopted by our societies as the most "natural" way to convey the passing of time, no doubt because it recalls the rotation of the planets and the apparent movement of the sun, our first timekeeper. There are, however, other ways to indicate time, such as a "jumping display", typically used to show the hour. It exchanges the hand for a disc inscribed with the hour numerals, visually similar to a calendar aperture. However, unlike certain calendars, each new indication is instantaneous. On each hour, the mechanism causes the disc to make one jump forward, then blocks it in this position until the following hour. Some watches also feature "jumping minutes", although jumping hours are more commonly paired with retrograde minutes.
Lap Timer	A function in a chronograph watch that allows the wearer to time segments of a race. At the end of a lap, the timer is stopped and then returns to zero to begin timing the next segment.
Lever Escapement	The lever divides into two pallets which lock and unlock the escape wheel teeth. Tthe action is governed by the balance engaging the other end of the lever, the escape teeth sliding on the inclined pallets life the lever to impulse the balance.
Liquid Crystal Display (LCD)	Liquid crystal display (LCD) watches show a numeric display continuously by means of the liquid held in a thin layer between two transparent plates. The numbers are made up of seven segments that form the number 8 when all are activated. They are activated by an electronic impulse.
Luminous	Luminous Hands and/or Hour Markers - is a standard feature on many watches. The hour markers and/or hands have a coating of "glow in the dark" which will illuminate in the dark so you can tell the time where there is insufficient light. Results vary by the amount & quality of Luminous material used.
Lugs	The arms of the watch case that hold the strap or bracelet.
Main Plate	The base plate upon which all other parts of a watch movement are mounted.
Mainspring	The coiled spring which provides the power to drive a mechanical watch movement.
Manual Wind Movement	A Manual watch operates by manually winding the crown which winds the mainspring in the barrel, thus powering the watch. Once wound it will stay working for the specified amount of time as indicated in your manual (generally 35-45 hours). See Automatic Winding Movement, Quartz Movement, Winding Crown
Marine Chronometer	A highly accurate mechanical or electronic timekeeper that is enclosed in a box and is used for determining the longitude on board a ship. Marine chronometers with mechanical movements are mounted on gimbals so they are in the horizontal position that is essential for their precision.
Measurement Conversion	A feature that allows the wearer to convert one type of measurement into another. It usually consists of a graduated scale on the bezel or dial.
Mechanical Movement	A "Mechanical Movement" is the term for watch that runs without an outside electrical source. The watch's mechanism is composed of multiple parts, gears, screws & springs. By winding the mainspring (either manual-winding or via automatic winding) the watch will begin to operate.
Micron	This is a thousandth of a millimeter and is a measurement used for the thickness of gold plating.
Minute Repeater	A watch that strikes the hours, quarters and minutes on gongs. The repeater is activated by a slide or button on the case edge. This is a highly complex achievement and increases the cost of the watch tremendously.
Mono (Single) Pusher Chronograph	A stop watch operated by a single button. While 99% of chronographs are operated by the use of two button - one to start & stop the stopwatch, the second to reset the stopwatch; a Mono Pusher complication allows for 1 button to start, stop & reset the stop-watch. See Split Seconds Chronograph a.k.a. Rattrapantte, Fly-Back Chronograph
Moonphase	A window in a watch which indicates the phases of the moon through 29 1/2 days. Some Moonphase watches incorporate a correction for the extra 44 minutes per month.
Mother of Pearl	The iridescent interior of a freshwater mollusc that is often used to decorate watch dials. Its colors include milky white, blue and pink. Mother of Pearl is available in an array of colors, such as blue, pink, yellow and more.
Movement	The motor of a watch that makes it keep time and perform functions. See Automatic Wind Movement, Manual Wind Movement, Quartz Movement.
Numerals	Numeral (Roman and Arabic) are used to present information in the dial and sub dials
Perpetual Calendar	A complication showing the date, day, month & leap year cycle at the minimum. Many will also display the year & Moonphase. This watch will correctly adjust for short and long months as well as 28 days of February once in 4 years. See Annual Calendar, Moonphase.
Platinum	Platinum is one of the rarest and most durable of precious metals. It doesn't tarnish and has a radiant, beautiful white luster. It is a popular choice for very prestigious watches & Limited Edition pieces.
Power Reserve Indicator	An indication of the state of wind in the main spring. A hand on the dial points to the number of hours the movement will work before it runs down. Also known as Reserve de Marche
Pulsimeter	A scale on a chronograph which is used for measuring pulse rate.
Push-Piece	A button that is pressed to work a watch function such as a chronograph, alarm or date corrector.
Quartz Crystal	Quartz is a piezoelectric material, meaning that it generates an electrical charge when mechanical pressure is applied. These crystals also vibrate when a voltage from an outside source, such as a battery, is applied. Piezoelectricity was discovered by Pierre Curie and his brother Jacques in 1880. In the early 1920's, W.G. Cady recognized that due to their elastic qualities, mechanical strength and durability, quartz crystals could be used to fabricate very stable resonators. Cady also concluded that the crystal could be cut in specific ways which would create resonators of almost any frequency that were practically independent of temperature variations. Quartz crystals were first used as a time standard by Warren Marrison, who invented the first quartz clock in 1927. Juergen Staudte invented a method for mass-producing quartz crystals for watches in the early 1970s.
Quartz Movement	This is an electronic watch movement with a quartz crystal that oscillates when a current is applied to it. The power to run the watch is normally provided by a battery or a capacitor. A quartz movement is generally more accurate than a mechanical movement.
Rattrapante Aka Split Seconds Chronograph	See Split Seconds Chronograph
Regulator or Regulateur	A Regulator display separates the minute and hour hands onto a separate axial & sub-dial. This allows for accurate time telling at a glance without the chance of having the watch hands covering each other.
Reserve de Marche	See Power Reserve Indicator
Retrograde	A watch with a retrograde display does not display the function in a circular fashion, as we are used to seeing. Rather, it sets out the functions in a linear manner. Instead of the hands going round in a circle, they travel along an arc, and when they get to the end, they jump back to the beginning
Rotating Bezel	A bezel around the watch that can be rotated. It has various timekeeping functions
Rotor	This is the oscillating part of an automatic watch that winds the mainspring.
Sapphire Crystal	Sapphire crystal is a very hard transparent material commonly used for "scratch-proof" watch glasses. Made by crystallizing aluminum oxide at very high temperatures, it is chemically the same as natural sapphire and ruby, but without the small amounts of other elements such as iron, titanium or chromium that give the gemstones their colors. Sapphire (whether natural or synthetic) is one of the hardest substances, measuring 9 on the Mohs scale, a system for rating the relative scratch hardness of materials. (Diamond measures 10, the highest rating, and the hardest steels are 8).
Screw Down Crown	Where the crown is threaded and tightens to the case by screwing the crown into a matching threaded tube that is part of the case. The crown has a gasket that is compressed & seals the opening when the crown is tightened - thus ensuring water resistance. A Screw-Down Crown is an essential feature for any watch you intend on swimming with. An additional benefit of the Screw-Down Crown is that the crown is somewhat more protected from accidental knocks. See Winding Crown, Crown
Second Time Zone Indicator	An additional dial that can be set to the time in another time zone. This allows the wearer to know the time in two zones simultaneously. See GMT Time, Dual Time, World Time
Shock Absorber	A resilient bearing which takes up the shocks received by the watch's balance staff and protects its pivots from damage.
Skeleton Case	A watch case with a transparent front or back, allowing visibility of the watch's movement.
Slide Rule aka Navigation Computer	A device consisting of a scale on the outer edge of a watch face which enables mathematical calculations such as fuel consumption, climbing times & converting miles into nautical miles or kilometers
Solar Powered Batteries	Batteries in a quartz watch that are recharged via solar panels on the watch face.
Split Seconds Chronograph Aka Rattrapante	A Chronograph with two centre seconds hands, the extra hand runs concurrently with the main chronograph hand but can be stopped independently then made to catch up with the running chronograph. Thus called the "Split Seconds hand" which refers to two hands - a flyback (Rattrapante) hand and a regular chronograph hand. Both hands move together with the ability to time laps or multiple finishing times, the wearer can stop the flyback hand while the chronograph hand continues. This, in effect, splits the hand in two. The split seconds thus allows recording the successive or additional times of events that start together.
Stainless Steel	A durable metal alloy that is almost rust resistant and rarely corrodes or discolors and, therefore, is highly suitable for watch case and bracelets. It is sometimes used on the case backs of watches made of other metals.
Stopwatch	See Chronograph
Stepping Motor	The part of a quartz analogue movement that moves the gear train and in turn moves the watch's hands.
Sterling Silver	Sterling silver is a highly reflective precious metal, which is 92.5% pure and is often used in watches & watch dials.
Subsidiary Dial	A small sub-dial on a watch face used for purposes such as indicating the date, power reserve or keeping track of elapsed time.
Swiss-Made	A watch may only bear the Swiss-Made label if the assembly work of the movement & watch was started, adjusted and controlled by the manufacturer in Switzerland. Furthermore, the law requires that at least 50% of the components of the movement be manufactured in Switzerland. The case & bracelet must not be manufacturered in Switzerland, however the parts must be delivered to Switzerland unassemebled and be assembled in Switzerland.
Swiss A.O.S.C.	A certificate of origin - a mark that identifies that a watch has been assembled in Switzerland and has components of Swiss origin.
Tachymeter Scale aka Tachometer	Common feature in chronograph watches. Measures the speed over a predefined distance. The wearer starts the chronograph when passing the starting point and stops it when passing the finish. The wearer can read the speed in units per hour off the tachometer scale. The scale is generally engraved on the bezel or printed on the outer diameter of the dial.
Tang Buckle	A tang buckle is a traditional Loop & Pin (belt type) buckle.
Tank Watch	A rectangular watch with bars along the sides of its face. It was inspired by the tracks of tank used in World War II and designed by Louis Cartier.
Timer	A device for registering intervals of time with out any indication of the time of day.
Titanium	A metal with a slightly darker/greyer appearance than Stainless Steel. Titanium is stronger and lighter than steel. Titanium is used increasingly in watch making, especially for sports and divers watches as it is resistant to salt water corrosion.
Totaliser	A mechanism that keeps track of and displays elapsed time, often on a subsidiary dial.
Tourbillon	The Tourbillon compensates for differences in rate caused by a watch adopting different positions. The principle is to mount the balance and escapement in a rotating cage. The balance & escapement rotate around their common axis going through all positions to average out the errors, Tourbillon cages or platforms usually rotate once per minute but 4 minute and six minute tourbillons are also found. The Tourbillon complication is an extremely difficult accomplishment to achieve & generally demands a high premium.
Uni-Directional Rotating Bezel	A bezel that can be rotated in one direction only and is used to monitor elapsed time. A ratchet mechanism is often in place to prevent it rotating in the other direction. It is often found on divers watches to prevent the diver from running out of air by overestimating remaining air supply if the bezel is accidentally moved from the original position. The fact that the bezel moves in one direction only is a fail-safe feature which means the diver can only underestimate remaining air supply.
Vibration Per Hour or VPH	This refers to the movement of an oscillating element that is limited by two extreme positions. The balance of a mechanical watch usually vibrates at a rate of five or six a second, more commonly recognized by (but not limited to) 36,000 28,800 or 18,000 vph
Water Resistance	A watch that is water resistant can withstand water to a certain extent. Check the watch manual to find out the exact level of water resistance your watch is. The "Water Resistant" feature is common on most watches. It is important to remember that the water resistant rating is granted when the watch is new & tested in ideal conditions. As the watch ages the seals & gaskets begin to erode these ratings decline. Therefore it is necessary to have the water resistance tested every year. Click here to read a detailed explanation about water resistance.
Winding	This is the action of tightening the mainspring of a watch. It can be done manually, by means of the crown, or automatically, via a rotor which is made to swing by the movement of the wearer's wrist.
Winding Stem aka Winding Crown	The grooved button on the outside of the case, used for setting the hands of the watch & the day and date of where applicable. It is also used for winding the mainspring of a mechanical watch. It is also known as the crown. See Crown
World Time Complication	A dial that tells the time of up to 24 time zones around the world. The names of the cities are printed on the dial. The hour in a particular zone can be read by looking at the scale next to the city that the hour hand is pointing to. The minutes are read in the normal way. The dial is usually found on the outer edge of the watch face. Watches with this function are called World Timers.