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Watch Terms Glossary

A
Acrylic glass
Acrylic glass is a synthetically produced, transparent material that can be easily shaped in certain temperature ranges. Acrylic glass is very weatherproof as well as breakage and corrosion resistant. Small scratches can be easily polished away.
Annual calendar
An annual calendar is a complication whose date only has to be corrected manually once per year at the end of February.
Anti-magnetic watch
An anti-magnetic watch remains uninfluenced by magnetic fields up to a certain strength and must also continue to run precisely to a certain degree after exposure. The norms DIN 8309 and ISO 764 set the standards for anti-magnetic watches.

According to DIN 8309, watches with a movement diameter larger than 20 mm count as anti-magnetic when they are unaffected by magnetic fields up to 4,800 A/m (6 mT) and deviate by no more than +/- 30 seconds a day.
Anti-reflective coating
An anti-reflective coating increases the transparency and clarity of watch glass. It reduces reflection, making it easier to read the watch.

Watchmakers create an anti-reflective coating by applying a thin, transparent layer to the watch glass under vacuum. Also known as AR coating.
Automatic
Automatic refers to the automatic winding of a watch caliber. The mainspring is wound by the motion of the wearer's wrist and arm. This happens in conjunction with a weight (a rotor), which oscillates and tenses the mainspring. A slipping clutch device is used on the mainspring in order to prevent it from being destroyed by too much tension. The central rotor mechanism is very widespread.
B
Bakelite
Bakelite is the trade name for a completely synthetic plastic created by the Belgian-American chemist Leo Baekeland in 1905. Objects such as steering wheels, radios, phones, and handles from pots and pants have been made from this heat-resistant material.
Balance spring
See hairspring
Balance wheel
The balance wheel regulates the beat of a mechanical watch through its constant vibrations, referred to as beats. It consists of a circular balance rim and in many definitions, the hairspring is considered a part of the balance wheel as well. The balance wheel takes over the job of the seconds pendulum found in grandfather clocks and wall clocks; however, it vibrates significantly faster. Today, normal speeds are either 21,600 or 28,800 alternations (beats) per hour, while a seconds pendulum only moves at 3,600 A/h. How precisely a watch runs depends on the number and regularity of the vibrations. The escapement gradually provides the balance wheel with energy from the mainspring, setting it in a back-and-forth rocking motion.
Bar
Bar is a metric unit of pressure which indicates how much weight is on a surface. Other units of measurement for pressure are the standard atmosphere (atm) or pascal (Pa).

1 bar = 100 kPa = 0.1 MPa

1 bar is about equal to the atmospheric air pressure on the Earth's surface or sea level pressure at a depth of 10 m.
Barrel
The rolled-up mainspring is located in the barrel. The mainspring stores the energy created when the watch is wound.
Bezel
The bezel is a ring that completely surrounds the watch glass. It can be rotatable or fixed. Diving watches feature a uni-directional rotatable bezel with minute markers for keeping track of the dive time. Chronographs often have a tachymetric scale on a fixed bezel in order to measure average speed. Bezels are typically made of metal or ceramic.
Bicompax
Bicompax refers to the number of subdials (totalizers) on a chronograph. A Bicompax layout has two subdials at 3 and 9 o'clock. A Tricompax has three, which form the shape of a V.
Bluing
Bluing refers to the process of heating steel components slowly up to 300 °C (572 °F). This causes an extremely thin, blue coating to cover the heated component. Watchmakers use this process in order to refine hands, screws, and other components. The process is commonly seen in watches produced in Glashütte, Germany.
Breguet balance spring
A Breguet balance spring is a balance spring with its last coil upraised, thereby reducing its curvature. It was invented by Abraham-Louis Breguet in 1795. Its concentric form allows the spring to "breathe" better and keeps the watch running more precisely. Also known as a Breguet overcoil, Breguet spring, or Breguet hairspring.
Butterfly clasp
Butterfly clasps are clasps which open at each end, extending the bracelet a significant amount and creating a wide opening.
C
Caliber
Caliber is another term for a watch movement. It's often used in combination with numerical watch names, such as "Caliber ETA 2824-2." Also spelled calibre.
Central seconds
A watch with central seconds has the second hand attached to the same center axis as the minute and hour hands. The counterpart to the central seconds is small seconds, where the seconds are displayed in a small subdial, usually at six o'clock. Small seconds are often found on chronographs which use the central second hand as the chronograph second hand.
Cerachrom
Cerachrom is Rolex's in-house ceramic. The high-tech material is particularly scratch-resistant and hard.
Chamfering (anglage)
Chamfering, also called beveling, is a complicated finishing method for watch movements where the edges are made to slope at a 45° angle and polished. The width of the edges remains the same.
Chiming mechanism
A chiming mechanism is a separate mechanism in a mechanical watch. A hammer hits a resonating body, such as a gong, to create the chimes, which tell the time via a series of sounds.
Chronograph
Chronographs have a stopwatch function, which can be used to time things such as sporting events.
Chronometer
Chronometers are especially precise calibers which have been certified for precision by an official body. Chronometer tests are predominantly carried out by the Official Swiss Chronometer Testing Institute (French: Contrôle officiel suisse des chronomètres, COSC). The Thuringian Office for Weights and Measures (German: Landesamt für Mess- und Eichwesen Thüringen) in Glashütte, Germany, also offers chronometer tests.
Co-axial escapement
The English watchmaker George Daniels invented the co-axial escapement in the 1970s as an alternative to the Swiss lever escapement. It gets its name from two escape wheels mounted on a shaft, one above the other. The advantage of this escapement is that there is a significant reduction in friction between the two wheels. Therefore, the escapement system requires less lubrication and runs longer before requiring maintenance. Omega further developed the co-axial escapement into a series of watches in the late 1990s. The majority of the current mechanical Omega watches have calibers with this escapement system.
Complication
A complication is an additional watch function. A moon phase, an alarm, a timing function, or a perpetual calendar are all common complications. They pose a challenge for watchmakers, especially when there are multiple complications in one watch movement.
D
Date display
The date is displayed either by a hand (date hand) or numerals printed on a ring which is hidden under the dial. A window on the dial creates an opening where the current date is displayed. Hands or a ring each make one full rotation within 31 days. When it's a month that has less than 31 days, the date display must be corrected manually.
Day of the week display
A day of the week display shows the current day of the week on the dial.
Diving watch
A diving watch (also referred to as a dive watch, diver's watch) is suitable for use while diving recreationally or professionally. The most common standards used for diving watches are ISO 6425 and DIN 8306. The watch must be waterproof to at least 100 m (10 bar). High-quality diving watches are usually waterproof to at least 200 m (20 bar), have luminous hands and indices, and have a bezel with minute markers. The bezel can only be rotated in one direction in order to avoid the wearer accidentally lengthening the dive time. Some diving watches can withstand depths of 1,000 m and greater; these usually have a helium escape valve as well.
Double barrel
When a caliber has two barrels, it may be described as double barrel. This extends the watch's power reserve.
Double chronograph
A double chronograph can time intervals. In order to do this, it has two chronograph second hands and three push-pieces. First, both second hands are started by pushing a push-piece. A second push-piece stops one of the second hands and allows you to read how much time has passed, while the other second hand keeps running. The third push-piece starts the stopped second hand again. Also known as a rattrapante chronograph, split-second chronograph, and split chronograph. Not to be confused with the flyback chronograph.
Dubois Dépraz
Dubois Dépraz is a manufacturer of watch complications.
E
ETA SA Swiss Watch Manufacturer
The ETA SA Manufacture Horlogère Suisse (ETA SA Swiss Watch Manufacturer) is a Swiss watch movement manufacturer belonging to the Swatch Group.
Escape wheel
The escape wheel is a part of a watch movement with a pallet fork's escapement. The escape wheel is located between the train and the balance wheel. The pallet fork creates the connection between the balance wheel and the escape wheel. A characteristic of the escape wheel is its asymmetrical teeth.
Escapement
The escapement ensures a steady, controlled release of the wound-up spring. The mechanism periodically locks the gear train, creating an even pace. At the same time, it transfers new energy to the oscillation system.

Today's wristwatches predominantly use the Swiss lever escapement, which consists of a pallet fork and an escape wheel. The escape wheel meshes directly with the seconds wheel (also known as the fourth wheel). The second hand is attached to the axle of the seconds wheel. The balance wheel swings back and forth and causes the pallet fork to uniformly move back and forth. Therefore, it can catch and lock the escape wheel with the pallet before releasing it and locking it again. This allows the wheel to move one tooth at a time. At a balance frequency of 28,800 A/h (4 Hz), this results in the second hand moving eight times.
Everose gold
Everose gold is Rolex's 18-karat rose gold alloy. Due to the use of platinum in the alloy, it should stay brilliant longer than typical rose gold. The pink color of the alloy comes from copper.
F
Finishing
Finishing (French: finissage) refers to the refinement of watch movements. Commonplace finishing includes decorations such as Geneva stripes, perlage, or sunbursts. Bluing screws and chamfering are also forms of finishing.
Flyback chronograph
A flyback chronograph has a special timing function. Once it's running, you can set it back to zero and start again at the push of a button. When a standard chronograph is running, on the other hand, it requires three pushes: one to stop the chronograph, one to reset it to zero, and one to start it again. Flyback chronographs arose from the field of military aviation. They're used when multiple consecutive maneuvers must be executed at exactly the right second. A normal chronograph could not fulfill this function, as the three pushes required to reset it would take too much time.
Folding buckle
The folding buckle is a mechanism for opening and closing a watch band. Unlike pin buckles, folding buckles open on a hinge. Straps with pin buckles, on the other hand, open entirely. Also known as a deployment clasp.
G
GMT
GMT stands for Greenwich Mean Time. It is the astronomically defined time in Greenwich, a district of London. It was originally used as the international civil time standard, but UTC (Universal Coordinated Time) has taken on that role since 1972. Unlike GMT, UTC is not an astronomically-based time.

A GMT watch displays the local time as well as the time in another time zone.
Geneva seal
The Geneva Seal is a seal representing the origin and quality of a caliber. Traditionally, the seal was stamped into the metal of the movement. However, a new method of nanostructural marking changes the metal on a microscopic level. Therefore, even very small individual pieces of a movement can carry the Geneva Seal. In order to have a Geneva Seal, the assembly, adjustment, and casing-up of a mechanical caliber must have occurred in the Canton of Geneva. There are 12 additional criteria relating to finishing, quality, and materials used which the caliber must also fulfill. Eight members from the Office for the Voluntary Inspection of Watches from Geneva (French: Bureau Officiel de l'Etat pour le contrôle facultatif des montres de Genève) are in charge of granting seal approval to watches. Cartier, Vacheron Constantin, Roger Dubuis, and Chopard are some of the most famous manufacturers whose movements have Geneva Seals.
Geneva stripes
Geneva stripes are straight, broad stripes that adorn movements and sometimes other watch components as decoration. Also known as Côtes de Gèneve or filets.
Guilloché dial
Guilloché dials feature guilloché finishing either engraved mechanically or by hand. Guillochés are intricate patterns made up of a series of interwoven lines.
H
Hairspring
The hairspring (also known as a balance spring) is a part of the balance wheel. It belongs to the oscillation system of a mechanical watch. It constricts and expands steadily multiple times per second and determines the watch's beat. The hairspring is thinner than a human hair and weighs only two milligrams. It's made of a special material, such as the alloy Nivarox or the anti-magnetic metalloid silicon.
Hand-guillochéd dial
Hand-guillochéd dials are dials which feature guilloché finishing engraved by hand. Since it's done manually, there are tiny irregularities in the pattern's lines.
Hardlex crystal
Hardlex crystal is a mineral glass predominantly used by Seiko. Thanks to a special process, it's harder and more scratch resistant than normal mineral glass. It lies between mineral and sapphire glass in terms of robustness.
Helium escape valve
A helium escape valve protects a diving watch from being damaged by excessive pressure. Professional divers breathe a special breathing gas mixture that includes helium in decompression chambers. The tiny helium atoms can find their way inside the watch case under pressure. This can cause the watch glass to pop out when the divers return to normal external pressure. The valve serves to equalize the pressure. It functions either automatically or manually.
Hesalite
Hesalite is Omega's name for Plexiglas. It's inexpensive to produce and replace and doesn't splinter.
L
Left-side crown
The wheel for setting the time and/or winding the movement is located on the left side of the case on a watch with a left-side crown. Most wristwatches have a right-side crown.
Limited series
A limited series is a series with a limited number of watches.
Luminous hands
Luminous hands are coated with a luminous material that glows in the dark. In the past, the radioactive substance tritium was used. The luminous effect is created when the crystals from the zinc compounds react with the electrons sent out by the tritium. Today, the main material used is Superluminova. This non-radioactive material is made up of inorganic, phosphorescent pigments called lume. Once a light source has sufficiently activated the pigments, they begin to glow. How long they glow depends on how long they were exposed to light. However, Superluminova has a limited charge.
Luminous numerals
Luminous numerals are coated with a luminous material that glows in the dark. In the past, the radioactive substance tritium was used. Today, the main material used is Superluminova. This non-radioactive material is made up of inorganic, phosphorescent pigments called lume. Once an artificial or natural light source has sufficiently activated the pigments, they begin to glow.
M
Mainspring
The mainspring, also referred to simply as a spring, stores energy and serves as an energy source for a mechanical watch. It's located in the barrel and is tensed by either manually winding the watch or, in the case of automatic watches, a rotor. The watch also has an escapement in order to prevent the mainspring from transferring all of its energy to the gear trains and balance wheel at once. Instead, the escapement ensures a controlled release over a period of days.
Manual winding
Manual winding is a type of watch movement winding. The mainspring is tensed by manually winding the crown (crown-wound). The spring continually transfers its energy to the train.
Mineral glass
Mineral glass is the standard material in the lower and mid-price ranges. It's comparable to window glass and harder than acrylic glass, but softer and less scratch resistant than sapphire glass. Mineral glass can be hardened to improve its qualities. Also known as mineral crystal.
Minute repeater
A minute repeater is a complication that tells the time audibly with chimes when you press a button. This incredibly intricate complication is also one of the rarest out there. A tiny chiming mechanism produces the chimes.
Month display
A month display shows the current month on the dial.
Moon phase indicator
A moon phase indicator is a watch complication that shows the phase of the moon as visible from earth on each day from the new moon to the full moon. One lunar month lasts 29 days, 12 hours, 44 minutes, and 2.9 seconds. The phase of the moon is displayed via a moving disc that shows through a window on the dial.
O
Original condition
A watch in original condition is a watch that is in its original state, completely unchanged.
Original parts
When a watch has original parts, it means that only official parts from the respective manufacturer were used when repairing and replacing parts in the watch.
P
Pallet fork
The pallet fork is a component of the escapement with two arms in the shape of a T. It connects the escape wheel to the balance staff. The pallet fork receives an impulse from the escape wheel and transfers it to the balance wheel. At the same time, it interferes with the movement of the escape wheel. Also known as a pallet lever or escape lever.
Perpetual calendar
A perpetual calendar is a watch complication that displays the correct date of the Gregorian calendar until the year 2100 with no corrections necessary. A perpetual calendar takes shorter and longer months and leap years into consideration.
Pin buckle
A pin buckle is a type of buckle for wristwatch straps. The longer end of the strap has holes punched in it. The shorter end has the actual pin, as well as a spring bar and a metal holder in the shape of a U, similar to a belt buckle. It functions in a similar fashion as well: The pin is inserted into one of the holes to achieve the desired length. The metal holder keeps the pin from coming out of the hole. Also known as a tang buckle.
Power reserve
The power reserve is the amount of time it takes the movement to come to a standstill after it was fully wound, without being rewound by hand or body movements.
Power reserve indicator
The power reserve indicator shows how much time is remaining until a mechanical watch loses power. It lets you know if and when the watch needs to be wound. The watch can be wound via the crown.
Precision index adjuster
A precision index adjuster helps keep a wristwatch running as precisely as possible. Watches are adjusted to different positions under different temperatures in order to get them running as accurately as possible. Chronometers are adjusted to five positions under three temperatures to fulfill the requirements of official chronometer testing centers.
Q
Quartz watch
Quartz watches are powered by a quartz crystal. The crystal is triggered by a current, which causes it to vibrate very fast at a constant rate of 32,768 times per second. The constant vibration is converted into electronic pulses, one per second. This drives a stepping motor to turn the gear wheels which control the watch's hands. Quartz watches from Asia took the world market by storm in the 1970s. They were sold in large numbers at attractive prices. They toppled the traditional watch industry during the so-called Quartz Crisis. The current necessary for the quartz watch usually comes from a battery or solar energy.
Quickset date feature
The quickset date feature, allows wearers to easily set the date with the crown pulled out. Movements without this feature set the date first after the hour hand has made two full rotations. Also called fast date correction.
R
Reference number
The reference number is equivalent to a model number in the watch world. It serves as the watch's unique identification. The reference number is helpful when searching for a certain watch, such as a vintage watch.
Rehaut
The rehaut is the chamfered edge of the dial that touches the watch glass. It's often used for scales and engravings.
Repetition
A repetition is a complication that tells the time via acoustic signals. A chiming mechanism is used in mechanical calibers. The mechanism receives its energy from an additional lever or push-piece on the edge of the case. There are five types of repetition: hour, quarter, half-quarter (one-eighth), five minutes, and minutes repetition. Repetitions increase the value of a timepiece, as they're especially complex to build.
Rolesor
Rolex uses the term Rolesor for watches which combine stainless steel and gold. The term "bicolor" is more commonly used when two different metals are used in a single watch.
Rotatable bezel
A bezel is a movable ring surrounding the dial and watch-glass found on certain types of watches, such as diving or pilot's watches.

Diving watches have rotatable bezels that can only rotate counterclockwise. This prevents the wearer from accidentally turning the bezel and lengthening their dive time. Before the dive, the diver synchronizes the zero marker with the minute hand. The 60-minute scale on the bezel allows them to then read how much time has passed.

Pilot's watches feature bi-directional rotatable bezels.
Rotor
The rotor is a flexibly mounted, half-round metal component that belongs to the winding mechanism of an automatic watch. When the watch moves, the rotor tenses the mainspring, winding the watch.
S
Sapphire glass
Sapphire glass is made of synthetically produced crystal. It's significantly harder and more scratch-resistant than mineral or acrylic glass and is therefore predominantly used in luxury watches.
Screw-down crown
A screw-down crown screws into the watch case securely. This mechanism offers improved waterproofness as opposed to crowns which are only pushed into the case. The Rolex Oyster, introduced in 1926, was the first wristwatch with a screw-down crown.
Screw-down push-pieces
Screw-down push-pieces screw, like a screw-down crown, into the watch case securely. The mechanism increases the waterproofness of the case. Screw-down push-pieces are often utilized on watches which are waterproof to extreme depths.
Sedna gold
Sedna gold is a reddish, 18-karat alloy made by Omega. It is composed of gold, copper, and palladium.
See-through case back
Luxury watches with see-through case backs have case backs made of sapphire or mineral glass. This allows you to view the movement in motion.
Shock protection
Shock protection is a system that protects fragile parts of the watch from damage caused by things such as dropping the watch or slamming it against a hard object. The balance wheel's pivots are especially delicate and susceptible to damage. A tiny metal spiral absorbs the shocks. A watch is considered shock protected when it can be dropped from a height of 1 meter onto a horizontal hardwood surface and suffer no damage. The most common shock protection system is Incabloc, although some manufacturers use their own systems.
Skeleton watch
A skeleton watch is a watch that displays its inner workings by not including the typical parts which conceal the movement. Skeleton watches or clocks are mostly fine pieces of art and are accordingly very complicated to create.
Small seconds
The small seconds is a subdial displaying the current seconds, usually located at six o'clock. These are often found on pocket watches, manual-winding wristwatches, and chronographs. The small seconds' counterpart is the central seconds, i.e. the second hand is attached to the same axis as the minute and hour hands in the middle of the dial. Also known as the subsidiary seconds dial.
Split-seconds chronograph
See double chronograph.
Spring
See mainspring
Stainless steel
Stainless steel refers to alloy or unalloyed steel with a particular purity level. When it comes to watches, it's important to use stainless steel in order to protect against corrosion.

Usually, 316L stainless steel is used in watch production. Rolex uses 904L stainless steel. These rustproof alloys contain chromium and nickel and are especially resistant to acids and moisture.
Stop seconds
Stop seconds allows you to set the watch to the exact second. When the crown is pulled out, the second hand stops moving. Once set to the correct time, you push the crown back into its original position and the second hand starts moving again.
Superluminova
Superluminova is the brand name for a green-glowing material used on hands and indices. The material charges when held under light and then glows in the dark. However, the luminosity fades over a period of a few hours. Superluminova is the most commonly used luminous material, although some manufacturers use other substances. Superluminova is non-radioactive, differentiating it from tritium and radium. Tritium and radium are radioactive substances which were previously the most commonly used luminous substances. Superluminova is also chemically stable, meaning it retains its luminosity for many years.
T
Tachymetric scale
Tachymetric scales are used to calculate units per hour. The scale is located on either the bezel or edge of the dial and is mostly used for calculating speed (km/h or mph). For example, if you drive a kilometer while timing yourself with your chronograph and it takes you 28 seconds, you can read on the tachymetric scale that your speed was 130 km/h. Famous watches with a tachymetric scale are the Omega Speedmaster Professional and the Rolex Daytona. Also referred to as a tachometer or tachymeter scale.
Telemeter scale
Telemeter scales are located on the edge of the dial of a chronograph and used to calculate distances. You can use a telemeter scale to measure how far away a storm is, for example. Using your chronograph, you start timing when you see lightning and stop it when you hear thunder. The large, stopped chronograph second hand will be pointing to the correct distance on the scale. The scale is also useful with artillery; you can use it to determine how far away enemy troops and their cannons are based on the time between the muzzle flash and the bang.
Tourbillon
A tourbillon is a round cage that rotates around itself one time per minute. The most important parts of a mechanical watch are located in this cage: the oscillation and escapement systems. Gravity influences these systems and causes small deviations when the watch remains in a vertical position. The fact that the tourbillon rotates around itself compensates for these deviations. Abraham-Louis Breguet invented the tourbillon in 1795 for pocket watches. Today, it's predominantly found in high-quality, expensive luxury watches. Producing a tourbillon demands a high degree of skilled craftsmanship.
Tricompax
The term tricompax refers to a certain arrangement of three subdials. They are in the shape of a V at 3, 6, and 9 o'clock on the dial.
W
Waterproofness
The waterproofness of a watch is displayed in bar. In addition to listing the watch's pressure resistance, the manufacturer often also lists its maximum depth. However, this value can be misleading: Watches waterproof to 30 m (3 bar) are actually not suitable for swimming, but rather only splashes of water. Diving watches are usually waterproof to at least 200 m (20 bar). The waterproofness is affected by more than just water pressure; temperature fluctuations can also be a factor. Waterproofness must also be checked regularly, as gaskets wear out. Water that has seeped into the watch usually appears as condensed water on the watch glass and can mean total ruin.
Winding mechanism
The winding mechanism winds the mainspring. Pocket watches used to require a key for winding the mainspring (key-wind). Later, this was replaced with the crown (stem-wind). In an automatic timepiece, an oscillating weight, the rotor, performs this function.
Y
Year display
The year display shows the current year on the dial.