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Watch Glossary

A

Alarm Feature
A feature on a watch which makes a sound or vibrates at a preset time.
Altimeter
A device which determines altitude by detecting changes in barometric pressure.
Analog Display:
A display which shows the time by means of analog hands.
Analog / Digital / Duo Display
A watch which displays the time using both traditional hour and minute hands coupled with a digital screen display. Also known as duo display.
Annual Calendar
A watch complication showing the day, date, and month. This watch will correctly adjust for short and long months; however, it will not account for leap year.
Aperture
A small opening/window on the dial which displays indications such as the hour or date.
Auto Repeat Countdown Timer
A countdown timer which resets and restarts once the preset time has elapsed. The countdown is repeated until the stop button is depressed.
Automatic Winding Movement
A mechanical watch which uses a weighted oscillating pendulum (also known as a rotor), to automatically wind the watch, thus eliminating the need for constant manual winding. The kinetic motion of the user's wrist causes the rotor to rotate, which in turn winds the mainspring. Once the power reserve is full, the timepiece must be worn daily for at least 8 to 10 hours to sufficiently self-wind and maintain the power reserve.

B

Bezel
A ring on the top side of the watch case encircling the crystal. Bezels can be fixed, have unidirectional rotation, or Bidirectional rotation. A functional bezel can be used to count down timing, measure a second time zone, as a tachymeter, and for navigation. Decorative bezels can be ornate, plain, or set with diamonds.
Bidirectional Rotating Bezel
A bezel which can be rotated clockwise and counter-clockwise, primarily used for keeping track of elapsed time.
Bracelet
A metal strap which secures a timepiece to a user's wrist. A watch bracelet is typically composed of steel, titanium, or gold. Bracelets typically have removable links which can be inserted or removed to adjust the length.
Buckle
A device used to fasten a bracelet or strap. The primary types of buckles are tang and deployment.

C

Calendar
A function which indicates day, date, month, and/or year.
Cambered
Refers to a domed or arched crystal.
Caliber or Calibre
Since the early 18th century, the caliber (often referred to in French as "caliber") 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 manufacturer.
Case
A metal housing which contains the components of a watch. The most common materials used are stainless steel, titanium, gold, and platinum.
Chronograph
A stopwatch function. A chronograph measures and displays elapsed times while allowing the watch to display conventional time. The chronograph mechanism is driven by the movement of the timepiece and is typically operated using two buttons on the side of the case which start, stop and reset the chronograph.
Chronometer
A precision watch with a movement that has been rated by the official Swiss testing laboratory "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 +/-0.07 seconds per day, due to the fact that quartz movements are more accurate in normal conditions.
Complication
A watch function other than timekeeping. Examples of a complication include chronograph, alarm, annual calendar, and/or GMT function, etc. Grand complication watches have higher function complications such as a perpetual calendar, tourbillon, minute repeater, equation of time functions, and/or other functions.
COSC
The official chronometer testing organization in Switzerland abbreviated COSC (Controle Officiel Suisse des Chronometres).
Countdown Timer
A feature which informs the user 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
A knob or button on the exterior of the case used for setting the time, date, and/or additional features. It is also used for manual winding of the mainspring for a mechanical watch. Also known as a "winder" or "winding stem".
Crystal
A clear cover on the watch case designed to protect the dial and hands. The crystal is typically comprised of glass, plastic, mineral crystal or sapphire crystal (a scratch-resistant synthetic material).

D

Day/Date
A watch which displays both the day of the week and the date of the month.
Day/Night or AM/PM Indicator
A feature which indicates whether the displayed time is AM or PM. This feature is most commonly found in watches with a GMT/dual time display or world time display.
Deployment/Deployant Buckle
An expandable, folding buckle which attaches to both sides of a strap. The buckle is opened to allow for the watch to fit over the user's hand, and then closed to secure the watch on the wrist. Once set, it need not be resized, thus reducing stress to the strap and elongating its life.
Dial
The face of the watch which displays the time.
Digital Display
A watch which displays time using an electronic digital display in place of analog. Liquid crystal display (LCD) is the most commonly used.
Dual Time
A watch which display local time and the time in at least one other time zone simultaneously. This is generally displayed by an additional hour hand. Some watches have a separate sub-dial showing the full clock at the additional time zone.
Duo Display
A display which shows the time both by analog and digital displays simultaneously. This is also known as an "AnaDigi" display.

E

Elapsed Time Rotating Bezel
A graduated rotating bezel which is used to keep track of segments of time. The bezel can be rotated so that the wearer can align the zero of the bezel with the minutes or seconds hands. The elapsed time can then be read off of the bezel.
EOL
An end of life battery indication in quartz-powered watches. Typically, the seconds begin to tick in 4 second increments while still maintaining the correct time. This notifies the wearer that the power is low and it is time to change the battery.
Escapement
A device at the heart of virtually all mechanical watches which provides the impulses to maintain the oscillations of the balance wheel or pendulum, which in turn governs the rate at which the wheels and hands of the watch revolve.

F

Fly-back Chronograph
A chronograph which restarts the instant it is brought back to zero without the need to stop, reset & restart the chronograph. This is particularly useful to pilots. Depressing the lower pusher only, a user can immediately reset the chronograph to time each successive leg of a search pattern. Without this feature, 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 tasks a watch can perform such as chronograph and countdown timer. These are also known as complications.

G

GMT Time Zone
Greenwich Mean Time (GMT) is also known as Zulu Time and UTC (Universal Time Coordinated). This standard, by which all world time is set, was agreed to at the 1884 International Meridian Conference in Washington, DC. 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. The term GMT is used with watches to refer to the ability of the watch to display local time and the time in at least one other time simultaneously, usually 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.
Guilloche
An engraving technique in which an intricate pattern or design is mechanically etched onto an underlying material with very fine detail. Specifically, it involves a technique of engine turning called "guilloche" in French. This is named for the French engineer "Guillot", who invented a machine that could etch fine patterns and designs on metallic surfaces.

H

Helium Escape Valve
A one-way valve which allows helium to dissipate from the case of a timepiece during decompression. Professional diver's 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 containing helium. Because helium is a small molecule, it will gradually seep through the O-rings into a dive watch over time in a pressurized diving bell. This is not an issue while at depth, however, decompression will adversely affect a timepiece if the helium is unable to escape. To prevent damage, diver's watches are equipped with a helium escape valve (or helium bleed valve) to release this extra pressure during decompression.
Horology
The science of time measurement, encompassing the art of designing and constructing timepieces.

I

Index Hour Marker
A simple stick/line design hour indicator on an analog watch dial, used in the place of numerals.

J

Jewels
Synthetic gemstones that act as bearings for the gear trains, reducing friction and wear.
Jump Hour/Minutes
A feature which uses numerals displayed through an aperture, which instantly change on the hour (or minute). Each hour, the mechanism causes the disc to make one jump forward and locks it in this position until the following hour. Some watches also feature "jumping minutes", although jumping hours are more commonly paired with retrograde minutes.

L

Lap Timer
A function of a chronograph watch which allows the wearer to time segments of a race. At the end of a lap, the timer is stopped and returns to zero to begin timing the next segment.
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 which form the number 8 when all are activated by an electronic impulse.
Luminous
Luminous hands and/or hour markers are a standard feature on most watches. The hour markers and/or hands have a coating of luminous material which will illuminate in the dark to assure easy viewing when there is insufficient light. Results vary by the amount and quality of luminous material used, as well as exposure to light during the day.
Lugs
The arms of the watch case which affix the timepiece to the strap or bracelet.

M

Manual Wind Movement
A manual watch mechanism which is powered by manually winding the crown. This winds the mainspring in the barrel, which in turn powers the watch. Once wound, it will remain operative for the amount of time as indicated in the user manual (typically 35-45 hours).
Mechanical Movement
A watch which operates without an electrical source of power. The mechanism is composed of multiple parts, gears, screws and springs. The watch is powered by manual winding or automatic winding of a mainspring.
Minute Repeater
A watch which 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 function, and watches featuring a minute repeater typically come with a high price tag.
Mono (Single) Pusher Chronograph
A stop watch operated by a single button. While most chronographs are operated by the use of two buttons to start and stop the stopwatch, a mono pusher complication allows for 1 button to start, stop and reset the stop-watch.
Moonphase
A feature of a watch which indicates the phases of the moon over 29 1/2 days.
Mother of Pearl
The iridescent interior of a freshwater mollusk which is often used to decorate watch dials. Its colors most commonly include milky white, blue, and pink, although rarer versions offer a wider variety of colors.
Movement
The engine of a timepiece which allows it to keep time and perform functions.

N

Numerals
Indicators in the form or Roman and/or Arabic symbols which are used to present information on the dial and/or sub-dials of a timepiece.

P

Perpetual Calendar
A complication showing the date, day, month, and leap year cycle at the minimum. Many will also display the year and feature a moonphase. This watch will correctly adjust for short and long months, as well as leap years.
Power Reserve Indicator
An indicator which displays the power level in the mainspring. A hand on the dial points to the number of hours remaining in the power reserve of the movement. Frequently referred to in French as "reserve de marche".
Push-Piece / Pusher
A button that is depressed to operate a watch function such as a chronograph, alarm, or date corrector.

Q

Quartz Crystal
A piezoelectric material which 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.
Quartz Movement
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.

R

Regulator or Regulateur
A display which separates the minute and hour hands onto a separate axial and 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 which lays out the functions in a linear display instead of the traditional manner. In place of the hands revolving in a circle, they travel along an arc. Once they reach the end, they jump back to the beginning and restart the cycle.
Rotating Bezel
A bezel designed to be rotated in one or both directions which can serve a variety of functions.
Rotor
A weighted, oscillating component of an automatic watch that winds the mainspring.

S

Sapphire Crystal
Sapphire crystal is a very hard transparent material commonly used for scratch-resistant watch crystals. Made by crystallizing aluminum oxide at very high temperatures, it is chemically similar to 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. In comparison, diamond measures 10 (the highest possible rating), while the hardest steels measure 8.
Screw-Down Crown
A crown which is threaded and tightens to the case by screwing into a matching threaded tube which protrudes from case. The crown's gasket is compressed and seals the opening when the crown is tightened, ensuring water resistance. A screw-down crown is an essential component of any watch intended for submersion. An additional benefit of the screw-down crown is that the crown is somewhat more protected from accidental opening.
Second Time Zone Indicator
An additional dial which can be set to the time in another time zone. This allows the wearer to know the time in two time zones simultaneously.
Skeleton Case
A watch case with a transparent front or back, allowing visibility of the timepiece's movement. Also known as exhibition case back.
Slide Rule/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, and converting miles into nautical miles or kilometers.
Solar Powered Batteries
Batteries in a quartz watch which are charged via solar panels on the watch face.
Split-Seconds Chronograph/Rattrapante
A chronograph with two center seconds hands. The additional hand runs concurrently with the main chronograph hand, but can be stopped independently and made to catch up with the running chronograph. 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 therefore allows recording of successive or additional times of events which start together.
Stainless Steel
A durable metal alloy which is rust resistant and rarely corrodes or discolors. This is the most common composition of watch cases and bracelets.
Sub-Dial
A small sub-dial on a watch face used to display addition indications, such as date, power reserve, GMT, moon-phase, etc.
Swiss-Made
A watch may only bear the "Swiss-Made" label if the assembly work of the movement and 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. It is not required that the non-mechanical components (such as the case and bracelet) be manufactured in Switzerland, however the parts must be delivered to Switzerland unassembled and be assembled in Switzerland.

T

Tachymeter Scale/Tachometer
A common feature in chronograph watches which 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 on the tachometer scale. The scale is typically engraved on the bezel or printed on the outer diameter of the dial.
Tang Buckle
A tang buckle is a traditional Loop and Pin (belt type) buckle.
Timer
A device for registering intervals of time.
Titanium
A metal which is stronger, lighter, and has a slightly darker appearance than steel. Titanium is used increasingly in watch making, especially for sports and diver's watches, as it is resistant to saltwater corrosion.
Tourbillon
A mechanism which compensates for differences in rate caused by a timepiece being in different positions in a three dimensional space. The principle is to mount the balance and escapement in a rotating cage. The balance and escapement rotate around their common axis going through all positions to average out the errors. Tourbillon cages or platforms usually rotate once per minute, however four and six minute tourbillons are also available. The tourbillon complication is an extremely intricate component, and typically demands a high premium.

U

Uni-Directional Rotating Bezel
A bezel which can be rotated in one direction only and is used to monitor elapsed time. A ratchet mechanism is often in place to prevent rotating in the other direction. It is often found on diver's watches to prevent the diver from running out of air by overestimating remaining air supply. The fact that the bezel moves in only one direction is a fail-safe feature which limits diver error to underestimate (and not overestimate) the remaining air supply.

V

Vibration Per Hour or VPH
A reference 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 5-6 times per second, more commonly measured in vibrations per hour (or VPH).

W

Water Resistance
A watch which is water resistant and can withstand a predetermined amount of exposure to moisture. This feature is common on most watches. It is important to remember that the water resistant rating is granted when the watch is new and tested in ideal conditions. As the watch ages, the seals and gaskets begin to erode and these ratings decline. It is therefore necessary to have the seals replaced and the watch tested annually.
Winding
An action of coiling the mainspring of a watch. This can be done manually by manipulating the crown, or automatically via rotor which rotates with the movement of the wearer's wrist.
Winding Stem/Winding Crown
A knob on the outside of the case used for setting the time and/or date of a watch. It is also used for winding the mainspring of a mechanical watch. Also known as the crown.
World Time Complication
A dial which tells the time of up to 24 time zones around the world. The names of the time zone representative cities are displayed on the dial. The hour in any time zone can be read by reading the scale next to the city to which the hour hand is pointing. Watches with this feature are called world timers.
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