Watch Glossary

Bezel
A watch bezel is the ring that surrounds the face of the watch and holds the crystal in place. The bezel can be decorative or offer additional functions. With ladies watches in particular, it is quite common to see diamonds, rubies, sapphires, or emeralds adorning the bezel. Among those bezels which rotate, there are two types: unidirectional and bidirectional. Bidirectional bezels can be turned in either direction; uni-directional bezels, usually intended for dive watches, move in the counterclockwise direction only. Such bezels are numbered 0-60 minutes with an arrow marker at 0, some count down and some count up. Another type of functional bezel commonly in use is the tachymeter bezel. Tachymeter bezels are fixed, and are seen on certain chronograph timepieces; they present a calibrated scale from which rates of speed can be quickly calculated.

Tachymeter

A tachymeter is a calibrated scale used to measure the speed traveled over a specific distance. The scale used for making this calculation is found on the bezel or the dial rim of a timepiece.
Bracelet/Strap
A watch bracelet is the cuff that wraps around the wrist, effectively making the timepiece a wristwatch. Metal bands are called bracelets. Leather, rubber or fabric bands are called watch straps.
Case Shape

tonneau

Tonneau is a shape for watch cases with convex sides. The tonneau case takes its name from the French word for "barrel".
Complications
The term "complication" refers to any watch function other than the basic timekeeping function. Examples would include calendars, chiming functions, alarms, indication of moon phase, and the tourbillon.

Alarm

An alarm watch is a mechanical timepiece that sounds an alarm set by the wearer. Most alarm watches have a feature that enables the wearer to set the alarm time (independent from the normal hour and minutes) and a function to start and stop the alarm. The alarm is driven by energy from a separate barrel distinct from the main power source of the watch. Alarm time is often displayed on a subdial, although some alarm timepieces simply have a single centrally-mounted alarm hand that the user positions between hour markers for an approximation of the alarm time to the nearest quarter hour; this operation is very similar to that of simple travel clocks.

Annual Calendar

More complex than a simple calendar, but less complex than a Perpetual Calendar. Automatically adjusts for months with different lengths (i.e. 30 or 31 days) with the exception of February--the only month in which the owner must manually intervene. Annual Calendar watches normally showcase indicators for date, day of week, and month with moon phase being a fairly common additional function. Unlike the Perpetual Calendar, it does not make allowances for leap year and the 4-year cycle.

Certified Chronometer

In fundamental terms, an instrument which measures time (a watch). More specifically, when applied to Swiss watches, the term "chronometer" denotes a highly precise movement which has undergone and passed a series of specific tests by an independent institute. The most well-known chronometer institutes are those of the C.O.S.C, or "Controle Officiel Suisse des Chronometres". Rolex, Omega, and Breitling are the Swiss brands which place greatest emphasis on the chronometer, although many other manufacturers obtain them as well, including Chopard, Ulysse Nardin, and TAG Heuer.

Chronograph

A stopwatch function enhanced with additional small dials indicating elapsed intervals (typically minutes and/or hours) for the specific event being measured. Buttons on the watch case control the stopping and starting of the chronograph function, as well as its reset back to "zero" when the operator is done timing something.

Flyback

A variation of the chronograph which gives additional sport-timing functionality. The mechanism of the flyback allows the central chronograph second hand to be safely reset to zero while it is in motion. By comparison, a normal chronograph in the middle of a timing sequence must be stopped and reset to zero before a new sequence is initiated.

GMT

GMT, an abbreviation for "Greenwich Mean Time", denotes that the watch has an indicator for a second time zone.

Grande Complication

This specific term refers to a very complex type of timepiece that combines three particularly prestigious complications. They are the perpetual calendar, the split-seconds chronograph, and the minute repeater.

Jump Hour

A jump hour function displays the hour in an aperture instead of a typical hand. The number in the aperture window "jumps" instantaneously to the next hour as the minute hand reaches the 60-minute position on the dial.

Minute Repeater

One of the most prestigious and difficult complications in watchmaking. Hammers strike carefully tuned gongs to mark off the hours, quarter hours and minutes acoustically. The most complex minute repeaters have three gongs (carillon), but most have two--a treble and a bass gong.

Moon Phase

A classical mechanism that tracks and displays the waxing and waning of the moon through its 29 1/2 day cycle. Usually, the moon's phase is depicted via a rotating disc with two moons oriented 180-degrees apart. The disc gradually advances through its cutout as the month passes, providing information on the progress of Earth's natural satellite.

Perpetual calendar

Perpetual Calendar watches have a complex mechanism that automatically adjusts for the different lengths of months, including February which can be 28 or 29 days depending upon whether it is a leap year or not. Perpetual calendars present indicators for date, day of week, month, and either the leap year cycle or century. Many perpetual calendar watches also incorporate a moon phase display, and some additionally show the calendar week.

Split Chronograph

The most complicated type of chronograph. The split chronograph, also known as Rattrapante, is characterized by two superimposed central chronograph hands, which travel in tandem. A dedicated button enables one chronograph hand to be stopped, while the other continues moving. This feature permits two separate intervals of time to be measured at once. Pressing the same button causes the split hand to immediately re-unite with its partner. The rattrapante can also function like a "normal" chronograph, when its added functionality is not required.

Sweep Second

The long centrally-mounted hand that denotes the seconds as it moves around the dial of an automatic watch is often called the sweep hand. By contrast, the motorized second hand of a quartz watch will click forward in distinct second-long increments.

Tourbillon

A very special and prestigious complication in a mechanical watch. A Tourbillon mechanism compensates for the effects of gravity on the balance, thus improving the overall accuracy of the watch. Originally invented by Abraham-Louis Breguet, the watch’s escapement (balance, lever and escape wheel combined) is housed in a lightweight cage which rotates on its axis over a specific interval of time, typically 60 seconds.

World Time

Refers to a travel watch displaying 24 world reference cities on an internal or external rotating ring. Once the worldtime ring is set according to the wearer's location, a glance at the ring keeps the wearer appraised of the time in key locations around the globe. This complication is particularly valued by international business professionals.
Dial Color

Skeleton

This term is used to describe the dial or caseback of a watch. It indicates that some or all of the mechanism is visible.
Dial Pattern/Texture

Guilloche

A special decorative texturing or machining of a surface on a watch, most commonly on the dial. This technique, also known as engine-turning can be stamped by a machine, or in the finest watches, executed by an artisan with aid of a traditional rose engine.
Features

Day/Night Indicator

In its simplest form, this indicator encircles the dial rim or the bezel of a watch that displays the time zones for key locations around the globe. The circle is shaded to show which time zones are in the day or night at any given time of the day. Certain watches display day/night indication in a small subdial with light and dark shaded areas. Although the principle is exactly the same, instead of rotating, these subdial indicators utilize a small hand to indicate the AM and PM hours.

Helium Valve

A helium valve, also known as a helium escape valve or HEV, is a feature found on professional dive watches. The helium valve is designed to release helium and other gases in specialized breathing mixtures that may have built up inside a watch during a deep water dive. Helium release valves can be either automatic or manually operated via a screw-down crown.

Military Time

Many watches have a subdial, scale or digital function for tracking time in the 24-hour format, as a supplement to the common 12-hour format. The 24-hour format is also known as military time.

Power Reserve

Denotes the number of hours of running time a mechanical watch has when its mainspring is fully wound. Certain timepieces feature an indicator that displays how much power is remaining. This indicator is often referred to as the "reserve de marche".
Water Resistant (m)
The design of a water-resistant watch helps prevent moisture from entering the case and harming the movement. Gaskets in materials such as rubber, Therban, or Viton around the case back, crystals, crowns and push-buttons seal these crucial points. Water resistance is tested in measurements of atmosphere (ATM). Each ATM denotes 10 meters of static water pressure. Many watch cases will list the basic measurement of 1 ATM as "water resistant." These watches will withstand small splashes of water but should not be worn while washing the hands or any other activity in which the watch risks immersion. Watches intended for regular or prolonged water usage have a minimum water resistance rating of 100 meters. Because water resistance is dependent upon the quality of the sealing materials, it is important to have watches evaluated periodically to ensure that their gaskets and sealing points are intact.