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From ‘alarm watch’ to ‘zodiac’…

The following pages are a glossary of terms associated with horology, watches and watchmaking.

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Deck Watch

A large-sized ship’s chronometer.

Deployment Buckle

A deployant, or fold-over clasp, allows for perfect strap closures through interlocking metal pieces

Depth Alarm

An alarm on a divers’ watch that sounds when the wearer exceeds a pre-set depth.

Depth Meter or Depth Sensor

A device on a divers’ watch that determines the wearer’s depth by measuring water pressure. It shows the depth either by analog hands and a scale on the watch face or through a digital display.


A progressive natural change of a watch’s rate with respect to objective time. In case of a watch’s faster rate, the deviation is defined positive, in the opposite case negative.


Face of a watch, on which time and further functions are displayed by markers, hands, discs or through windows. Normally it is made of brass – sometimes silver or gold. Dials come in an almost limitless variety of shapes, decorations and materials.

Digital Watch

Said of watches whose indications are displayed mostly inside an aperture or window on the dial.

Divers Watch

A diver’s watch is designed for underwater diving and will typically have a water resistance of around 200 to 300 m (660 to 980 ft). Dive watches will have a unidirectional rotating bezel with 15 or 20 minute markings and a screw-in crown and backplate.

Metal bracelets or rubber straps (not leather) are used as they are adequately water (pressure) resistant and able to endure the galvanic corrosiveness of seawater. Bracelets are often fitted with a divers extension deployment clasp by which the bracelet can be appropriately extended by approximately 20 mm to fit over a wetsuit.

Dive watches generally have a relatively thick sapphire crystal to enhance the pressure-resistance of the watch. Some watches intended for diving at great depths are fitted with a helium release or helium escape valve to prevent the crystal from being blown off by an internal build-up of helium pressure seeping into the watch case. This can happen when decompression stops during resurfacing are not long enough and a pressure difference builds up between the helium in the watch and the environment.

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Incomplete (jeweled or non-jeweled) watch movement without regulating organs, mainspring, dial and hands. It is also known as a blanc roulant.


A name for a patented power mechanism found on some Citizen watches. This mechanism uses ordinary light to keep a rechargeable battery powered for watch operation. This technology is very sophisticated allowing some watch models to remain powered for up to 5 years in the dark. Watches with Eco-Drive technology will never need to have the battery replaced.

Elapsed Time Rotating Bezel

A graduated rotating bezel used to keep track of elapsed time. The bezel can be turned so the wearer can align the zero on the bezel with the watch’s seconds or minutes hand. After a period of time passes, you can read the elapsed time off the bezel. This saves you having to perform the subtraction that would be necessary if you used the watch's regular dial.

Electroplating Process

Process of covering metal articles with a film of other metals. The article is immersed in a chemical solution; electric current (D.C.) flows through the solution from a piece of metal (anode) to the article (cathode), depositing metal thereon by electrolysis. See also PVD.


Undrilled jewel, placed on the balance jewel with the tip of the balance-staff pivot resting against its flat surface, to reduce pivot friction. Sometimes used also for pallet staffs and escape wheels.


A surface decoration usually applied to the dial and the rotor using a grooving tool with a sharp tip, such as a rose engine, to cut an even pattern onto a level surface.

Equation of Time

Indication of the difference, expressed in minutes, between conventional mean time and real solar time. This difference varies from -16 to +16 seconds between one day and the other.


A mechanism that is fitted between the gears and the regulating organ. The combination of the balance, balance spring, pallets and escape wheel, a subgroup which divides the impulses coming from the spring barrel into small, accurately proportioned doses. It guarantees that the gear train runs smoothly and efficiently.

Escape Wheel

A wheel belonging to the escapement mechanism.

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The usually inclined ring that separates the crystal from the dial. The flange is sometimes equipped with features such as tachymetric scales and pulsometers.


Engraving on the dial or case of a watch, covered with an enamel layer.


Said of surfaces worked with thin parallel grooves, mostly on dials or case bezels.


Feature combined with chronograph functions, that allows a new measurement starting from zero (and interrupting a measuring already under way) by pressing down a single pusher, i.e. without stopping, zeroing and restarting the whole mechanism. Originally, this function was developed to meet the needs of pilots.

Fold-over Clasp

Hinged and jointed element, normally of the same material as the one used for the case. It allows easy fastening of the bracelet on the wrist. Often provided with a snap-in locking device, sometimes with an additional clip or push-piece.

Fourth Wheel

The seconds wheel in going-train.


Generally defined as the number of cycles per time unit; in horology it is the number of oscillations of a balance every two seconds or of its vibrations per second. For practical purposes, frequency is expressed in vibrations per hour (vph). See also Vibration.


A conical part with a spiral groove on which a chain or cord attached to the barrel is wound. Its purpose is to equalize the driving power transmitted to the train. Almost all 16th, 17th and 18th Century watches have a fuse.

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Thin plate of glass or transparent synthetic material, for protecting the dial of the watch.


Bronze and beryllium alloy used for high-quality balances. This alloy assures high elasticity and hardness values; it is non-magnetic, rustproof and has a very reduced dilatation coefficient, which makes the balance very stable and assures high accuracy of the movement.


GMT, or Greenwich Mean Time, is based on the globe being divided into 24 time zones as established in the London Meridian Conference of 1884. The zero meridian runs through the Royal Observatory in the London suburb of Greenwich. In contemporary watch terminology, GMT is often used to describe a wristwatch that displays a second time zone or a 24hour indication.


Harmonic flattened bell in a steel alloy, generally positioned along the circumference of the movement and struck by hammers to indicate time by sounds. Size and thickness determine the resulting note and tone. In watches provided with minute-repeaters, there are often two gongs and the hammers strike one note to indicate hours, both notes together to indicate quarters and the other note for the remaining minutes. In more complex models, equipped also with en-passant sonnerie devices, there may be up to four gongs producing different notes and playing even simple melodies such as the chime of London’s Westminster Clock Tower or ‘Big Ben’ as it is commonly known.


A surface decoration usually applied to the dial and the rotor using a grooving tool with a sharp tip, to cut an even pattern onto a level surface. The finished effect is guilloché.

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Steel or brass element used in movements provided with a repeater or alarm sonnerie. It strikes a gong or bell (s).


Indicator for the analogue visualization of hours, minutes and seconds as well as other functions. Normally made of brass (rhodium-plated, gilded or treated otherwise), but also steel or gold. Hands are available in different shapes and sizes and take part in the aesthetic result of the whole watch. Early watches only had one hand for the hours.

The most common hand forms are:
• Baton – straight hands that taper to a fine point. These are the most basic and common hands used on most watches today.
• Daupine – are in the form of an elongated triangle
• Feuille – a hand in the shape of a leaf
• Poire
• Skeleton
• Spade
• Sword

Hardlex Crystal

is Seiko’s trademarked name for a hardened mineral crystal

Harrison (John)

John Harrison was born in 1693 in Foulby, West Yorkshire and lived for most of his life in Barrow upon Humber. He became a carpenter, like his father, was a gifted musician and a self-taught watchmaker, creating his first timepieces entirely out of wood.

He moved to London in the 1750s, at the height of his development of his “sea watches” and died in the capital in 1776. The ship’s chronometers were rediscovered at the Royal Greenwich Observatory in the mid-20th century and restored.

Today the H1, H2, H3 and H4 are on display at the National Maritime Museum in Greenwich. The H5 is owned by the Worshipful Company of Clockmakers, and is displayed in the Clockmaker’s Museum in London’s Guildhall.


Heart-shaped corn, generally used to realign the hands of chronograph counters

Helium Valve

Valve inserted in the case of some professional diving watches to discharge the helium contained in the air mixture inhaled by divers. The helium escape valve prevents the crystal from being blown off by an internal build-up of helium pressure seeping into the watch case.


An artificial glass made of a plastic resin. Back in the 1960’s, many watches used either mineral glass or acrylic crystals. These are not difficult to scratch, but very inexpensive to replace. Now though, most all luxury watches use the highly scratch resistant synthetic sapphire crystals, there are some styles/brands that use the Hesalite (a trade name for an advanced synthetic (acrylic) crystal). The reason for this is directly related to the watch's certification for use in high stress/impact situations. While sapphire crystals are less prone to scratching, they can be shattered. When shattered, they break into tiny fragments that would be hazardous in some environments e.g. NASA specify hesalite crystal for all watches going into space. The Hesalite crystal is shatterproof so is maintained on some specific models as a safety feature.

Hunter Caliber

A caliber characterized by the seconds hand fitted on an axis perpendicular to the one of the winding stem.

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