Watch Glossary

Some of the varied and wonderful terms associated with horology, watches and time.


Anti Meridian, Before noon.


An audible signal at a given preset time, or at the end of a timed period.


A display that uses hands rather than a digital readout.


A type of watch mechanism shielded against string magnetic fields to maintain accuracy.


The fixing of numerals and other features to the face of a watch.


An opening in the face of a watch to enable display of information such as date, day and moonphase.

Anti reflection

A treatment often applied, particularly to sapphire crystal watch glass, which reduces reflections and makes the watch easier to read.


Connected to the mainspring of a movement. It is the oscillation of the balance that provides the energy and rhythm of the watch.

Battery Reserve Indicator

(See also Power Reserve indicator and Reserve de Marche.) –  A method of displaying that the battery in a quartz watch is running low. This will often take the form of less frequent “ticking” e.g. Every 2 seconds.


The circular portion of the case of a watch surrounding the crystal or glass. The bezel of the watch often displays information including speed on a tachymeter, time units on a dive or GMT watch or slide rule elements on pilot’s watches. On other watches the bezel my be purely decorative.


Convex in French. Used to describe a convex design element of a watch or clock. 


A metal watchband typically made up of links of a design unique to the particular watch. Available in many types of alloy, including stainless steel, platinum, titanium and gold. Used universally for both men’s and women’s watches.

Butterfly Clasp

See Deployant Clasp. A clip which opens in two directions, expanding to enable easier putting on and removal of a wristwatch.


Display on a watch face of day/date sometimes month/day/date, referred to as a triple calendar.


Has a number of meanings within horological circles. Can refer to the size of a watch movement. Most often used to referring to the model or series of movement within the catalogue of a particular manufacturer. A Calibre may have meanings such as type of movement, series, period of manufacture etc within the one number.


The housing within which the movement of a watch sits. This may form part of the decorative aspect of a wristwatch. A caseback may be clip-on or screw-down, and can in fact be transparent revealing the movement inside.


A watch with a stopwatch function that enables the timing period to be controlled.


A standard of classification conferred by the COSC (See below) giving a watch certification as having a high degree of accuracy under a number of operating conditions.


The configuration of having two hands running on the same axis. The terms has become more commonly associated with a technology, popularised by Omega, which reduces the amount of friction in the escapement assembly of a mechanical watch movement.


A function included in a watch movement that performs a function additional to displaying hours, minutes and seconds, eg calendar, moonphase, chronometer etc. See also Grand Complication.

Contrôle Officiel Suisse des Chronomètres

(COSC) – The official Swiss testing institute that verifies and certifies a watch movement’s accuracy. To achieve Certified Chronometer status a movement is tested for 15 days under a range of conditions including temperature and position to confirm accuracy. Variation tolerances vary with conditions but must have an average daily rate of -4/+6 seconds.   

Côtes de Genève

Machined oscillating decorative pattern on the flat surfaces of a watch movement


Most often found at “3 O’clock” the crown is a knob used to wind and set the watch. May have multiple positions for setting date, and other complications as well as time. Bull-head watches feature a crown located at “12 O’clock” with “4 O’clock also being a popular location. Some “lefty” models feature a crown at “9 O’clock”.


The “glass” window in the front of a watch. Crystals are made from different materials chosen for their individual properties.


Rolex term for a small lens in the glass/crystal used to magnify date elements on the face of a watch.


A watch and/or movement that shows both the day and date.


A type of buckle or clasp attached to the band or bracelet of a watch consisting of several hinged parts that open and expand to more easily put on and take off the watch. Sometimes referred to as a butterfly clasp.


The portion of a watch face that shows the values of various displays, eg Hours, Minutes, Seconds etc.

Display back

A watch casing with an open back, most often covered with glass, that allows the movement of the watch to be viewed.

Dual Time Zone

A watch that is capable, by means including several hour hands on the one face or several dials on the one face, of displaying more than one time zone at once eg The Rolex GMT Master 2 can show one time on its main face and another time can be independently set on the 24 hour hand.


Swiss manufacturer of mechanical movements. Although held in the highest regard as an OEM supplier, their movements are available in watches retailing well under $1000 up to tens of thousands.


The mechanism within a watch movement that converts the stored power in the spring to drive energy in the watch. The frequency of an escapement’s oscillations is referred to as frequency. This is the portion of a mechanical movement that produces the fast ticking sound.


The use of engraving on the surface of a watch, then covered with enamel to form a decorative surface.


A surface of a watch, eg dials, bezel or face carrying thin parallel grooves.

Full Rotor Automatic

An automatic winding watch movement which allows for the complete revolution of the winding rotor.


Abbreviation for Greenwich Mean Time. When used to refer to a feature of a watch, two or more time zones are displayed using separate hour hands.


Curved lines interlaced to form a patterned surface.


Moving indicators on the face of a watch showing dial values such as hour, minute, date, power reserve etc. Many defined styles of hands exist, bearing different shapes for both aesthetic and practical purposes. Clear readability being popular on tool watches such as diving, pilot and military watches, and more decorative styles prevalent on dress watches.

Helium Escape Valve

Divers watches are often fitted with a HEV. Air with a higher helium component is used in diving applications conducted at great depths. Helium, having a smaller molecular size than other air elements, can move in and out of a watch casing regardless of seal. When depressurising, either in open water or even a pressurised cabin helium can become trapped inside the casing, blow out the glass/crystal and damage components. A helium escape valve allows one way movement of expanding helium to escape the casing.


The study of time and watches.


Incabloc is the trademarked name for a shock protection system in mechanical watch movements. By mounting the balance wheel hub jewel using a springed element the potential damage to this critical component is lessened. Invented in the 1930s, it is a widely used system in many mechanical movements even now.


Watch makers have long used jewels, (often synthetic ruby), to create wear resistant hubs for rotating components of a watch movement, also used for other components subject to constant wear. Modern variations on the ruby include the Diapal system in Sinn watches which diminishes the need for servicing of these components by using harder diamond parts in place of the softer ruby.


A system whereby the movement of the wearer creates kinetic energy stored as electricity. Similar to automatic only electrical rather than mechanical kinetic energy. Kinetic is used specifically by Seiko to refer to this type of system although other brands use movement to generate and store electricity to run non mechanical watches.


Protruding sections of a watch casing to which a watch band or bracelet is attached using spring bars.

Lug Width

The distance between lugs on a watch case. Lug width can dictate the width of a strap or bracelet which can be attached to a watch, varying its look and style. Typically modern sports watches trend toward a wider style with dress and older watches bearing a finer look. Over time, with a move to larger casing and face sizes, lug width has also grown.


Emitting light from within. Commonly reffered to in watch circles as “lume”, luminescent hands and markers are used on watches so that they can be read in the dark. Many types of luminescent materials are used, including the very slightly radioactive Tritium. Watches using Tritium must carry a “T” on the face of the watch.


A coiled spring of metal ribbon that stores kinetic energy which powers a mechanical watch movement.

Manual Wind

A mechanical movement that must be wound by hand using the crown to store energy in the mainspring to keep running.


Indicators on the face of a watch to mark out time, indicate hours etc.


A mechanical watch converts energy stored within a spring to motion within a watch movement to display information on its face.

Minute Repeater

An auditory way of telling time. When a button is pressed a series of tones is heard signifying hours and minutes. Using a complex system of differing sized bells and hammers, a repeater is mechanically one of the most elaborate types of complications included in a watch movement. This intricacy makes watches bearing repeaters rare and usually very valuable.

Moon Phase

A complication on a watch that displays the current phase of the moon. Moon phases is often included on watches with other date related complications including date, day and month. These watches are referred to as Triple Date Moonphase, and in better brands tend to be sought after for their complexity.


The inner workings of a watch that convert either spring (mechanical)  or battery (quartz) energy into the information displayed on its face.


New In Box. Also LNIB, Like New In Box.

New Old Stock

A Mint condition/New watch first available for initial sale a long time ago but never used and/or sold. NOS watches are highly sought after by collectors for their condition and rarity.

Perpetual Calendar

A highly complicated movement displaying calendar information that adjusts to different lengthed months and leap years. Perpetual calendars are often among the most valuable, highly sought after watches.

Power Reserve/Reserve De Marche

A display on the face of a watch showing the remaining time left in the spring before requiring further winding.


A mineral with a highly regular molecular vibration rate. Quartz is used in watches as its vibrations can be harnessed to control the output with great accuracy.

Quick set/date

A movement that allows the date to be set directly from the crown of the watch rather than the rotation of the time.


Split lap time function on a mechanical chronograph. Separate second hands are utilised to show split lap times.


See Minute Repeater


A retrograde hand does not move through a full 360 degrees, instead it will move back to the start of it’s “sweep” begin again. Commonly used to indicate day or date.


A weighted component of an automatic watch movement, the rotation of which creates energy which is stored in the mainspring.


The red jewel used to prevent wear on some moving and contact parts in a mechanical movement. Rubies may be either synthetic or actual stone.

Spring Bar

Small sprung bar used to attach bands and bracelets to the case of a wristwatch.


Smaller dial on the face of a watch to display information such as seconds, dual timezone, chronograph times etc.

Screw-down Crown

The crown of a watch that screws on/in to the case to better seal the watch. This ensures more water and dust resistance.


Called both the most beautiful and the most ugly form of mechanical movement in watchmaking, the skeleton watch is one constructed so as to enable all moving parts to be viewed. Although many watches feature a crystal back and front, the skeleton movement is constructed and cut so that each moving part of the  movement is visible.


Man made sapphire crystal used for its hardness and scratch resistant qualities to ensure clear viewing of a watches face.

Screw Back

Threaded back for a watch casing to ensure a more secure seal and attachment.

Sweep Second Hand

Second hand which moves around the face of a watch. Depending on the mechanical construction, the sweep motion on a second hand may vary from a smooth glide to fast “ticking”. It is rare that a mechanical watch will feature a once a second tick, although some do exist as a speciality.


Instrument for measuring speed over a measured distance.  Also called a Tachymeter. Time an event that takes less than 1 minute. The scale on the Tachometer will tell you how many of those events will occur in 1 hour.
e.g.  A racing car covers 1 mile in 30 seconds. The sweep seconds hand, when stopped at the end of the mile, would point to 120 on the tachometer. The average speed of the car is 120 m.p.h.

Tool Watch

A watch designed for use under specific physical conditions such as diving, flying etc. A tool watch bears specific functionality that relates to its use case such as displaying elapsed time, yachting start countdown timer, a slide-rule bezel, depth gauge. etc. Tool watches tend to be of sturdy construction and design to reflect their intended use.     


A watch mechanism where the entire escapement assembly rotates mechanically to counter the pull of gravity on the weighted balance wheel. The tourbillon was invented at a time when pocket watches were worn and sat in one position most of the time in a pocket. Due to their mechanical complexity, watches with a tourbillon mechanism fitted tend to fetch high prices new and older models are highly sought after and very valuable. 


A watch face with 3 sub-dials, traditionally at 3, 6 and 9 o’clock, most often displaying seconds, minutes and hours elapsed.

Triple Calendar

A watch face that displays the day, date and month.


A slightly radio-active isotope of hydrogen that collects light and is used to allow the hands or hour markers to glow in the dark. The radiation is so low that there is no health risk. Watches bearing tritium must be marked with the letter T on the dial near 6 o’clock.

Two Tone

Most often 18K gold and steel or white gold, two tone refers to a multicoloured watch design.

Uni-directional Rotating Bezel

A bezel that indicates elapsed time, often found on divers watches.  It moves only in a counter-clockwise direction.  If a diver is timing remaining air supply and knocks the bezel by mistake it can only move in one direction so that any error can only be on the side of safety.

Water Resistance

Ability to withstand water pressure. The watch case joints are made to prevent moisture or liquid entering. Regular servicing is necessary and recommended to maintain full integrity of the seals. Water resistance is measured in meters and refers to the depth that the watch will keep out water when properly maintained.


The process of tightening the mainspring of a watch movement, this can be manual via the crown or automatic via the movement of the wearer.

Yacht Timer

A complication which displays a countdown of the 5 minutes between the warning signal and start of a sailing race. This appears as 5 circles which change colour, most often at the top of the face.