Glossary of Watch Terms
Acrylic crystal: An inexpensive type of plastic made from natural gas and petroleum used to protect the face and dial of a watch. What's great about acrylic is its flexibility, it doesn't shatter on impact, scratches can be easily polished out and it doesn't promote glare. However, it isn't as long-lasting or durable as Sapphire or Mineral.
Adjusted: A movement can be adjusted for temperature, wearing positions, and isochronism, which refers to keeping the time rate immune to the gradual loss in power from the wind-up to wind-down motion of a mainspring. Basically, all adjustments are made to keep the time rate of a movement uniform.
Altimeter: An instrument used by aircraft to measure altitude. The altimeter measures atmospheric pressure much like a barometer does but, unlike a barometer, it's made to represent pressure changes in altitude.
Amplitude: This refers to the measurement of the rotation or swing in a watch movement's balance wheel, typically expressed in degrees. The amplitude of a watch movement depends on what position it's in. For example, if a watch is lying flat it's amplitude will be around 270 to 315 degrees, and if it's in a vertical position the amplitude will be less due to friction. The reason amplitude is measured is because it affects the accuracy of a watch, if amplitude is too low the watch will run faster and vice versa.
Analog watch: A watch that uses the constant motion of a few rotating pointers (i.e. minute & hour hands) pointing to numbers on a circular dial to tell time. The term analog watch was coined when digital watches were first being introduced and there was a need to distinguish them from their counterparts (e.g. traditional hands & dial watches)
Analog-digital display: A watch which features two displays, an analog display (minute & hour hands), and a digital display (numbers) to show time.
Annual Calendar: Refers to a complication that displays the hour, date, and sometimes year and moonphase. Although very similar to the perpetual calendar, the annual calendar only adjusts for month's with 30 or 31 days, and not for leap years or the 28 days of February. Because of this, a watch with an annual calendar must be changed once a year on the 1st of March.
Anti-magnetic: This means your watch can, to a certain level, be exposed to magnetic fields with little to no time deviation (e.g. without affecting its accuracy). If your watch is mechanical, magnetic fields from microwaves, refrigerators, stereo speakers, x-rays, phones, iPads, computers, hairdryers, homeopathic magnetic bracelets, televisions, and a myriad of other devices all have the potential to affect its proper functioning. One of the most vulnerable watch parts is the mainspring, a very tiny and delicate metal coiled spring which functions as the main power source of a watch. When affected by magnetism, its individual coils will stick together, shortening the spring, and in effect, making the watch run faster.
Aperture: a small opening cut into a watch dial to show the hour, date, day, moon-phase etc..
Applied Indices: Raised metal batons or numbers joined to the watch dial. The pins are usually pressed, glued, or soldered.
Art Deco: The predominant design style from the 1920's to 1930's. Most rectangular and barrel shaped watches were inspired by this period.
Atmosphere (ATM): A rating for water resistance. One ATM equates to ten meters water resistance, although this doesn't take into consideration how movement affects water pressure. For example, if your watch says something like "10 ATM/100 meters" you may think you can go deep sea diving but the water resistance rating was tested in move-less water, which doesn't account for water pressure increases due to movement like currents etc...
Auto Repeat Countdown Timer: A countdown timer that restarts all over again every time the preset time has finished. So, if you set the countdown to finish after 30 minutes the countdown will start again after those 30 minutes are complete. It's ideal for timing workout repetitions.
Automatic Watch: Also known as the self-winding watch, the automatic watch uses motion to power itself. This is done with a metal weight connected to the movement called a rotor, which rotates when subject to motion, and in doing so winds the mainspring automatically. Of course, if the automatic watch hasn't been subject to any movement in a while it will need to be winded manually.
Auxiliary Dial: Simply, any extra smaller dial to the main dial.
Balance Spring or hairspring: In a mechanical watch, it's the very fine tightly coiled spring attached to the balance wheel which coils and recoils, in and out, creating an oscillation, controlling the speed at which the wheels of the watch turn, and finally the rate of movement of the hands.
Balance Wheel: An oscillating wheel, kept in motion and rate by the hairspring, responsible for keeping the watch's accuracy.
Barrel: A circular or drum shaped container which holds the mainspring for a mechanical watch. Its size determines how much power reserve will last.
Battery/Power Reserve Indicator: A gauge on a watch dial indicating either how much power a watch has before you have to wind it again, or how much battery is left for a battery powered watch.
Bezel: This refers to a ring shaped object located either on the outside or inside of the crystal of a watch. Used for tracking time zones (GMT), determining heart rate (pulsometer), calculating speed (tachymeter), and various other functions.
Bi-directional Rotating Bezel: A type of bezel that can be moved clockwise and counter-clockwise. Used for calculating elapsed time.
Breguet Overcoil or Spiral : An improved version of Dutch mathematician Huygens' flat balance spring created by Abraham-Louis Breguet in 1795. The Breguet over-coil or "spiral" is different in that instead of the balance spring being traditionally flat, its last coil is raised up and over to the top of the spring, nearing its center point. This reduces the effects of gravity on the hairspring, making the balance wheel oscillate more harmoniously, and thereby maintaining the watch's accuracy.
Bridges: A plate or bar attached to the main plate that forms the frame capable of housing all the inner workings of a mechanical.
Cabochon: A non faceted, smooth, decorative gemstone cut into a round convex shape. Sometimes, for decoration, they're placed on winding crowns.
Calender display: Simply, a watch that displays the day, date, month, or year. There are several types of calendar displays, some of which even display the lunar cycle.
Caliber / Calibre: This usually refers to a watch movement and its model type. For example, Rolex "caliber 1570".
Case back: The "back" or underside of a watch.
Chapter Ring: The ring on a clock or a watch dial indicating the minutes and hours. These could be engraved, attached, printed, and in some cases not even have numerals but just indices, like a stick dial.
Chronograph: A watch with a stopwatch function. Most modern watches will have a sweeping seconds hand to show elapsed seconds, and a few sub-dials to show elapsed minutes and hours.
Chronometer: Originally, this referred simply to an instrument that measures time. Today, it's used as a title to indicate a watch's exceptional accuracy. For a watch to be called a chronometer it needs to have been awarded a certificate by the official Swiss chronometer testing institute in Switzerland, or from any other official neutral body. For a watch to obtain such a certificate it must undergo a series of tests such as being placed in various positions for several days and subjected to different temperatures.
Complication: Any feature in a watch beyond the hour and minutes display. For example, chronographs, calendar displays, moon phase displays, alarms etc...
COSC: The Official Swiss Chronometer Testing Institute responsible for certifying the precision and accuracy of wristwatches. This is done by putting each individual watch through a rigorous 15-day testing protocol, included being put in 5 positions, and different temperatures.
Countdown Timer: A function that keeps track of how much a pre-set period of time has passed. Sometimes, this feature comes with a warning signal that will alarm you seconds before the time runs out.
Crown: The button or knob on the outside of a watch responsible for setting the time, date and a variety of other functions. It's also responsible for winding manual mechanical watches. Other words used for crown are winder, winding stem and pin.
Crystal: The clear protective cover placed over the watch dial. Made from either glass, synthetic sapphire, acrylic or mineral.
Cyclops: A small magnified lens, either molded into the crystal or glued to it, used to make the date on a dial more readable.
Day/Date: A watch that features the day of the week and the date.
Depth Alarm: An alarm that goes off when you have exceeded a pre-set depth.
Dial: It's the "face" of the watch which displays time using markings or numerals.
Diver's watch: Typically, a watch with a water resistance rating of 200 meters. Although, to be considered as a serious contemporary diver's watch it must conform to the test standards set by the ISO 6425, the International Organization for Standardization. Those watches that do conform are marked with the word DIVER's.
Ebauche: A movement from an external supplier in an unfinished state, without any wheels, pinions, or other component parts. Movements in this condition have been bought then refined and reworked from some of the most famous name brands in the watch industry. This is due to the enormous difficulty involved in making movements on a large scale from scratch. In the vintage watch collecting field a lot of "no name" watches are called ebauche.
Elapsed Time Rotating Bezel: A bezel used to track how much time has gone by. This is done by aligning the arrow on the bezel with the minutes or seconds hand. A common function among chronographs and dive watches.
Elinvar: A hairspring made from a nickel-iron alloy. A material known for not being affected much elastically by temperature. This makes for a more durable, accurate movement.
Escapement: The mechanism in a mechanical watch responsible for transferring power from the mainspring to the balance wheel in a controlled & regulated manner. In other words, it regulates the motion of the watch hands.
Fly-back Chronograph: In order to restart a regular chronograph you have to press the button once to stop the timer, a second time to return it to zero, and finally a third time to start it again. With a fly-back chronograph all you have to do press the button once and it will stop the timer and reset it to zero.
Frequency: The speed at which a watch beats or ticks, expressed in either hertz or vibrations per hour. Contemporary mechanical wristwatches have a frequency of 28,800 VpH (4Hz).
Function: A utility or tool.
Gasket: A small, air tight sealed ring made of either plastic, neoprene, or rubber between the case-back and case used to keep water and dust from damaging the movement inside the watch.
Gear Train: It's the system of gears responsible for transmitting power from the mainspring of the watch to the escapement, controlling the motion of the hands.
GMT Time Zone: Stands for Greenwich Mean Time, a 24 hour scale, refers to the international standard of time for every part of the world except the United States. This international standard was developed so that travelers could know the time almost anywhere in the world by either adding or subtracting from it to get the local time. Watches with this function usually have one hand to display the time in 12-hour form, and a separately adjustable 24-hour hand. With these two additional hands you can know the time in any two time zones.
Gray Market: The proper term is "parallel imports". This refers to watches that weren't originally meant to be sold in the USA, but meant for a different world market. The upside to buying a watch from this market is it's discount prices, the downside is that the watch will not have a manufacturers warranty.
Guilloche: An decorative engraving usually done on watch dials characterized by patterns of interlaced lines.
Hacking Seconds: Also called stop seconds. This refers to a watch with a seconds hand that could be stopped when the watch's crown is pulled out. This allows you to easily synchronize your watch with another.
Haute Horlogerie: In French Haute means "high", and Horlogerie means horology, so this translates to high study or art of watchmaking. In the watch community the term refers to high-dollar timepieces.
Helium Escape Valve: A feature found on many dive watches, used to release trapped gases in a watch when there's a critical pressure build up.
Horology: The study or science of measuring time, which involves the art of making timepieces.
Hunter Case: A pocket watch that can be opened up in the front like a door.
Index Hour Marker: It's the hour indicator on a normal analog watch, used as an alternative to numerals or markers.
Indices: Also called applied or applique indices. This refers to the raised metallic batons or numbers joined to the watch dial.
Jewels:The synthetic rubies or sapphires that function as bearings for the gears in a watch movement, minimizing friction.
Jump Hour/Minutes: An indicator that displays the hour or minute using a window instead of the usual hour and minute hands.
Kinetic: A line of Seiko watches that uses a quartz movement without a battery, powering itself through a capacitor using the movement of your wrist.
Lap Timer: A function on a chronograph that allows you to time parts of a race. At the end of every lap you stop the timer, which then returns it to zero and restarts it.
LCD: A liquid contained in a thin layer between two clear plates used to display the time in a digital watch
Lever Escapement: The most common escapement for watches today. Preferred because of its exceptional shock resistance, and high accuracy.
Lugs: The part of a watch used to attach a watch band or bracelet.
Luminescence: Simply, any watch dial which illuminates in the dark.
Mainplate: The bridges as well as the mainplate hold the components of a watch movement together. The majority of every calibre is made up of the mainplate which acts as the base of the movement.
Manual Wind Movement: A watch that requires you to wind it manually everyday to keep it running.
Marine Chronometer: A timepiece that you can use to work out longitude while at sea.
Measurement Conversion: A watch bezel with a graduated scale which allows you to convert one type of measurement into another.
Mechanical Movement: A movement powered by a mainspring
Micron: Refers to the unit of measurement for the thickness of gold coating. 1/2 micron (20 millionths of an inch)
Minute Repeater: A complication that allows you to hear the time through a series of chimes by pushing the slide lever on the side of the case.
Moonphase: A complication that tracks the current phase of the moon in our lunar cycle.
Mother of Pearl: The shining iridescent material which forms the inner layer of the shell of some fresh water mollusks used on some watch dials for decoration.
Perpetual Calendar: This refers to a watch that displays the day, date, and month. But, unlike the annual calendar which requires you to set the date once a year, the perpetual takes into consideration leap years, knows every day of the month, and will not need to be adjusted until the year 2100.
Platinum: A rare precious metal known for its durability. Watches with platinum are among the most desirable, along with stainless steel and solid gold.
Pulsometer: A scale located on the dial or bezel used to determine one's pulse.
Pusher: The button that is pushed to work a mechanism.
PVD: This refers to a process called Physical Vapor Deposition, used for coating a surface, in this case a watch, with materials like hard ceramic, gold, diamond-like carbon, or silicon oxide. Basically, the watch is placed in a vacuum chamber, where the coating material is vaporized then condensed, penetrating the surface of the watch with the material.
Quick Set / Quick Date: To get an idea, a non-quick set watch requires that you rotate the hour hand, by popping out the crown, to change the date. There are two types of quick sets, the single-quick set and the double. The single quick set requires you to rotate the hour hand to change the day. The double-quick set allows you to change the day and the date without having to rotate the hour hand.
Rattrapante / Split Seconds Chronograph: A type of chronograph that allows you to set two timers at once, given that they start simultaneously.
Regulator: This refers to a watch that displays the hours, minutes, and seconds on separate dials.
Repeater: A watch function that allows you to audibly chime the hours or minutes at the push of a button.
Retrograde: Refers to any semi circle shaped dial or sub-dial.
Sapphire Crystal: A synthetically processed crystal chemically similar to ruby and natural sapphire, but without those elements which give it its color. Sapphire crystal is made by administering extremely high pressure and heat to aluminum oxide powder. The crystal is transparent, very durable, scratch resistant, and nearly as hard as diamond. On the Mohs scale, used for measuring relative scratch hardness, sapphire crystal is at a 9, and diamond a 10.
Screw-down crown: A watch with a crown that locks into place with the case. This seals the crown into the case, preventing water from entering, and accidental tugging of the crown.
Shock Resistance: The mark on a watch's case-back that tells you how well it copes with external shocks. For a watch to be considered shock resistant it must adhere to the minimum standards set by the International Organization for Standardization or ISO. The ISO standard is based on a test, in which a watch is dropped onto a hardwood floor a meter high. If the watch still keeps good time afterwards, it can officially be marked with the words "Shock Resistant".
Skeleton Watch: A watch with a see-through case-back.
Small Seconds Dial: A sub-dial that displays the seconds, separate from the main minute and hour display.
Spring Bar: This refers to the little bar between the watch lugs used to fasten a watch band.
Stepping Motor: The component of an analog movement in a quartz watch that moves the gear train and thus the hands on the dial.
Sterling Silver: Sterling silver is a combination of 7.5 percent copper and 92.5 percent silver. The reason for this combination is that pure silver is too fragile to be applied to watches. By adding copper to the mix its hardness and durability is improved significantly. The material is commonly found on watches and watch dials.
Sub-Dial / Subsidiary Dial: A small additional dial featured on some watches used for indicating the date, tracking elapsed time and for a variety of other functions.
Sweeping Seconds Hand: Most vintage watch collectors understand this to mean a watch with a seconds hand that sweeps (i.e keeps moving) and doesn't tick. Although, historically it meant a watch that displays its seconds hand on the center dial instead of the sub-dial.
Swiss A.O.S.C: This means a watch has been put together in Switzerland with parts that come from Switzerland.
Tachymetre / Tachometer: A scale imprinted on the bezel or inner bezel of an analog watch used to calculate average speed or distance.
Tang Buckle: A watch band designed like a classic belt buckle.
Tank Watch: This refers to a rectangular shaped watch with bars running through it, meant to resemble the tracks and shape of a tank. Originally, the tank watch was a line introduced by the French watchmaking company Cartier. In 1917, the idea was conceived by Louis Cartier, who was inspired by the Renault tanks he saw on the western front during the Great War.
Tonneau Case: This refers to a barrel shaped watch. In the wine trade it refers to a large wine barrel equal to 59.44 U.S. gallons.
Tourbillon: A device that mounts the watch's escapement in a small revolving cage to overcome the effects of gravity, allowing for precision in a mechanical watch.
Tritium: A low radiation substance used to illuminate parts of a watch dial.
Uni-directional rotating bezel: Simply, a scale used to show elapsed time which can only move counterclockwise. This type of bezel is usually found on dive watches as a precautionary measure. For instance, If a diver is keeping track of his air supply and accidentally knocks his bezel it can only move counterclockwise.
World Time Complication: Commonly located on the outer rim of the watch face, this tells the time up to twenty-four time zones globally. It's used by checking the scale next to a city's name, then adding or subtracting that number from the local time.