Acrylic is a type of plastic that was used to make crystals before harder materials like synthetic sapphire became available. It is usually thicker and easier to scratch than a sapphire crystal.

A complication that uses sound and sometimes vibration to alert the user at a pre-set time. Most often found in quartz watches, but occasionally in mechanical ones too.

Each clockwise and anti-clockwise turn of the balance wheel travels through a set angle of rotation - this angle is called the amplitude, and is set between 275 and 315 degrees.

A watch that has both analogue displays (hands) and digital displays (numerals). Often powered by quartz movements, but there are odd exceptions.

A method of representing time using a continuously varying display, most commonly with rotating or pivoting hands.

The practice of adding an angled chamfer to the edges of plates and bridges for decorative and functional purposes. Functionally, it removes sharp edges, preventing damage during service and thus eliminating debris falling into the movement.

A complication that automatically corrects the date for months with 30 and 31 days, only needing adjustment between February and March.

The cut-out in the dial used to view the date wheel.

A measure of pressure used to define water resistance in Atmospheres. As water depths increase, so does pressure, and thus the pressure-resistance of the watch needs to be stronger to stay sealed. 10 ATM is the equivalent of 100 metres.

A movement that can be wound both with the crown and by an oscillating weight that spins with the movement of the wearer's wrist.

A wheel around a centimetre in diameter set with a hairspring. It is part of the escapement and helps to feed power from the mainspring back into the movement in controlled, regulated bursts by spinning repeatedly clockwise and anti-clockwise.

The stubby cylindrical container in the movement that houses the coiled mainspring. Some watches only have one, some have more, usually indicating a higher power-reserve.

The foundations of the movement onto which the rest of the movement is attached. The dial is mounted on the underside.

A matt finish achieved by firing many tiny glass beads at high pressure.

Each rotation of the balance wheel, either clockwise or anti-clockwise, is one beat. The average mechanical watch oscillates at around 28,000 beats per hour.

The practice of adding an angled chamfer to the edges of plates and bridges for decorative and functional purposes. Functionally, it removes sharp edges, preventing damage during service and thus eliminating debris falling into the movement.

The protective metal ring around the edge of the watch crystal that can be removed from the case for repair or replacement. Some bezels have the ability to rotate in either one or both directions as a timing or time zone function.

Steel can be decorated and protected against corrosion using a technique called 'bluing,' which turns it blue. It can either be done by using the traditional method of heating or the more recent method of chemical treatment.

The base of the movement onto which the rest of the movement is attached. The dial is mounted on the underside.

Beats per hour. Each rotation of the balance wheel, either clockwise or anti-clockwise, is one beat. The average mechanical watch oscillates at around 28,000 beats per hour.

A watch strap comprising of a chain of linked solid pieces, usually made from metal.

The outer-most coil of the balance wheel hairspring is twisted back over the top of itself and pinned half way along the width of the coil. This is to prevent deformation of the spring during expansion and contraction to keep an even and stable oscillation. Invented by Abraham Louis Breguet.

A plate secured to the movement by at least two screws.

A finish achieved using spinning brushed wheels of varying grades - appears as many fine scored lines over the finished surface.

A hinged pin retainer used to latch one end of a strap to the other.

The Contrôle Officiel Suisse des Chronomètres, the Official Swiss Chronometer Testing Institute that independently verifies the accuracy of tested movements.

A complication that displays the date, day, month and sometimes, year.

A specific model or design of movement.

The housing in which the movement, dial and hands are contained, usually made of metal.

The push-fit or screw-down cap on the rear of the case. Often fitted with a display glass to view the movement through.

The middle section of a three-piece watch bracelet link.

A spacer used to fill the vertical void between the edges of the dial and crystal, often with minute markers applied to it.

A complication that allows the user to measure a specific period of time from zero.

A movement that, when tested by an independent official body, falls within the accuracy parameters set by that body.

A secure folding system used to fasten a bracelet together, usually made of metal.

A type of escapement patented by the late George Daniels in 1980 that considerably reduces friction and the need for lubrication.

A cantilevered metal plate secured to the movement at one end only.

A wheel found in chronographs whose shape is like that of a castle turret. More difficult to make than a standard lever or cam mechanism, a column wheel coordinates the engagement of the chronograph using gear meshing rather than vertical friction.

A function in a movement. Complications vary from simple - time and date for example - to complex, like a perpetual calendar.

A type of decoration often found on movement plates, usually consisting of tightly packed curved lines engraved along the length of repeating thick strips.

The knob used to control the movement from the outside of the case for time and date setting and movement winding.

Distended shapes protruding from the case that protect the crown from being knocked.

The clear glass that allows the user to see the dial. Older watches will have a crystal made from acrylic, newer ones from mineral glass or synthetic sapphire.

A half-way house between a rectangular case and a round case.

A complication that displays the days of the month as a number.

A complication that displays the days of the week as a word.

The incremental movement of the seconds hand once each second. Seen normally on a quartz watch, and is complicated and rare on a mechanical watch.

A complication that strikes the hours, number of ten minute periods since the hour andminutes on command using a series of gongs.

The application of finishes to beautify a watch or its components.

A secure folding clasp similar to those found on bracelets for use with material straps.

The display portion of the watch from which the time and other functions can be read.

A caseback with a glass window fitted for viewing of the movement.

A folding additional link in a bracelet that allows a diver's watch to fit over a diving suit without the use of tools.

Diamond-like coating. Normally black in colour, it is a chemically-deposited coating used to colour and protect metal. Much harder and more scratch resistant than PVD coatings, but not scratch-proof.

A mechanism that rotates the tourbillon cage and escapement through a second axis as well as through the traditional first.

A chronograph that uses two second hands simultaneously to measure split times.

The links that marry the bracelet with the case.

A complication that measures the difference between apparent solar time and mean solar time.

A wheel with barbed teeth that engages with the pallet fork. It is part of the escapement and helps to feed power from the mainspring back into the movement in controlled, regulated bursts by being locked and released by the pallet fork.

The part of the movement that controls the release of the mainspring's power, made up of the balance wheel, pallet fork and escape wheel. As the balance wheel oscillates back and forth, it rocks the pallet fork from left to right, catching and releasing the escape wheel such that it turns a small amount each time, thus regulating the power of movement.

A caseback with a glass window fitted to it for viewing of the movement.

The appearance of a subtly decorated material; polished, brushed or bead-blasted for example.

A complication that strikes the hours and number of five minute periods since the hour on command using a series of gongs.

A chronograph complication whose seconds hand can be immediately reset and restarted during active timing.

A tourbillon mechanism that is supported by a cantilevered bridge (called a cock) rather than a traditional spanning bridge.

A chronograph complication that displays seconds in 1/8th segments.

A complication that displays the date, day, month that only requires adjustment on a leap year.

A measure of repetition per second in Hertz (Hz), for example the number of oscillations of a balance wheel.

A conical spiral gear upon which a chain winds.

A thin piece of material, usually rubber, that is compressed between two components to create a seal.

An arrangement of different sized cogs, aligned to achieve a desired speed of rotation.

The official seal of the city of Geneva, Switzerland, given to watchesthat meet an extremely high standard of construction and finishing.

A type of decoration often found on movement plates, usually consisting of tightly packed curved lines engraved along the length of repeating thick strips.

Greenwich Mean Time, the original standard of time and still the basis upon which all other time is calculated.

A complication that strikes the hours on command, and also the number of hours and quarters every quarter, using a series of gongs.

An intricate and precise creation of mathematical patterns using engraving.

The ability to stop the seconds hand when setting the time for more accurate time-setting.

The coiled spring fitted to a balance wheel that allows it to bounce clockwise and anti-clockwise repeatedly.

A stamped code on precious metals to pinpoint its origin and authenticity.

A long, slender indicator that travels progressively along a scale to indicate a measure or unit.

A mechanical movement that requires rotation of the crown to wind the mainspring.

The brand name for Omega acrylic crystals.

Helium Escape Valve. Developed by Rolex alongside the commercial diving company COMEX, the HEV was an automatic valve that allowed gas to escape from a watch during decompression to prevent the crystal from popping off.

The study of time.

A brand of spring-loaded shock protection used on balance wheel-supporting jewels to absorb sudden, potentially damaging impacts.

Markers on the dial indicating incremental units.

Bearings with high wear resistance and low friction made from rubies. Modern jewels are synthetic.

An hour indicator that makes instantaneous jumps between hours rather than the more traditional gradual progression from one to the next.

Liquid crystal display. Used to display images, commonly numbers or text, in a digital format.

The horned prongs extending from the top and bottom of a watch case onto which the strap is fixed.

A material, most commonly a paint, used on watches to produce a visible glow in low light. Historically made with radioactive materials like radium and tritium, now made with non-radioactive materials.

A brand that produces non-radioactive luminous paint.

The base of the movement onto which the rest of the movement is attached. The dial is mounted on the underside.

A coiled length of metal strip that provides power to the movement once wound.

A mechanical movement that requires rotation of the crown to wind the mainspring.

The first portable clocks accurate enough from which to calculate longitude.

Consisting of clockwork parts with no electrical assistance.

A self-winding, oscillating weight smaller than a standard, full-size rotor.

A cheaper alternative to synthetic sapphire for watch glass, but not as scratch-resistant.

A complication that strikes the hours, quarters and number of minutes since the quarter on command using a series of gongs.

A complication that displays the stages of waxing and waning through the lunar cycle.

The engine that powers and drives a watch.

A thin piece of material, usually rubber, that is compressed between two components to create a seal.

A lever with two prongs at one end that are each mounted with a synthetic ruby tooth. It is part of the escapement and helps to feed power from the mainspring back into the movement in controlled, regulated bursts by rocking back and forth to lock and release the escape wheel.

A decoration that comprises of repeated overlapped circular graining, usually on metal.

A complication that displays the date, day, month and year and does not need adjusting until 2100 when the leap year will be ignored.

A hinged pin retainer used to latch one end of a strap to the other.

A round gear, usually the smallest in a gear train.

A smooth finish that has mirror-like properties.

A measure of remaining energy in a movement. Also a complication that displays the remaining energy in the movement.

Buttons used to activate complications such as a chronograph. These should not be operated in wet environments or when the watch is submerged.

Physical vapour deposition. A thin chemical surface treatment that is used to apply solid colour to a material, usually metal. Not as hard or as scratch-resistant as DLC.

A complication that strikes the hours and number of quarters since the hour on command using a series of gongs.

The second-most abundant material in the Earth's crust, used, with an electrical impulse, to produce even oscillations from which to measure time.

A feature that allows the date to be independently adjusted via the crown, without having to manually wind the hands through full twenty-four hour periods.

A heavily radioactive material used to produce luminescent paint on watch dials in the early part of the 20th century.

A chronograph that uses two second hands simultaneously to measure split times.

A complication traditionally used by yachtsmen to count down the ten minutes before the start of a race.

The adjustment of a movement's beat to improve accuracy.

A spacer used to fill the vertical void between the edges of the dial and crystal.

A complication that strikes the time on command using one or more gongs.

A non-circular, linear scale whose indicating hand instantaneously returns to the beginning when it reaches the end.

An oscillating weight that spins with the movement of the wearer's wrist to wind the mainspring.

Bearings with high wear resistance and low friction made from rubies. Modern rubies are synthetic.

A matt finish achieved by firing sand at high pressure.

A water-resistant seal created between the crown and the case using a thread and o-rings.

Spring-loaded shock protection used on balance wheel-supporting jewels to absorb sudden, potentially damaging impacts.

A method of timekeeping used by astronomers to keep track of the night sky's orientation.

The method of reducing a component, most commonly the movement, to its barest minimum, thus creating the effect of a layered skeleton.

A watch, usually quartz, that is capable of drawing and storing charge from light.

Spring-loaded tubes used to secure a strap to a case by pinning it between the holes in the lugs.

The threaded bar that connects the crown to the movement.

A band that secures the watch case to the wrist.

A smaller dial located within the main dial.

A watch containing many complications.

A brand of non-radioactive luminous paint.

A description of the smooth, continuous motion exhibited by the seconds hand on a traditional mechanical movement, as opposed to the staggered ticking of a quartz-powered seconds hand.

An extremely hard and scratch-resistant material used to make watch glass.

A dial marker that indicates the use of radioactive, tritium-based luminous paint that emits less radiation than the legal limit of 25 millicuries (mCi).

A scale, usually marked around the edge of the dial or bezel on a chronograph watch, that can be used in conjunction with the chronograph seconds hand to measure speed.

A region with a set standard of time, independent of other regions. Usually set based on the relative position of the region on the Earth's surface.

A half-way house between a rectangular case and a round case.

A complication that rotates the escapement around one or more axes to compensate for the effects of gravity on accuracy.

A radioactive material used to produce luminescent paint on watch dials in the mid-20th century.

A method of timekeeping that tracks a whole twenty-four hour day as one continuous scale.

Coordinated universal time. The official standard of national time, based on GMT.

Each rotation of the balance wheel, either clockwise or anti-clockwise, is one vibration. The average mechanical watch oscillates at around 28,000 vibrations per hour.

Vibrations per hour. Each rotation of the balance wheel, either clockwise or anti-clockwise, is one vibration. The average mechanical watch oscillates at around 28,000 vibrations per hour.

The ability to retain a seal when submerged in increasing depths of water, expressed as a rating of depth in metres (m) or pressure in Atmospheres (ATM).

An alternative name for the gears used to transfer power through a movement.

An alternative name for GMT, used by the military.