The watch glossary.
Every term you will meet on a spec sheet or in a review, explained in a sentence or two, with a link to the full guide where we have one.
- Automatic
- A mechanical movement that winds itself through a rotor turned by the wearer’s motion. Read more
- Annual calendar
- A calendar complication that needs correcting only once a year, at the end of February. Read more
- Ana-digi
- A watch that combines analog hands with a digital display for functions such as dual time, alarms and timers. Read more
- Atomic timekeeping
- A watch that sets itself from a radio time signal, so it can stay accurate without manual correction. Read more
- Balance wheel
- The weighted wheel that oscillates on a hairspring and sets the pace of a mechanical watch. Read more
- Bezel
- The ring around the crystal. It may be fixed or rotate, and can carry a timing, 24-hour or tachymeter scale.
- Bund strap
- A leather strap with a pad under the watch, originally issued to German military pilots.
- Caliber
- The model name or number of a movement, such as NH35 or Powermatic 80.
- Caseback
- The back cover of the case. A display or exhibition caseback has a crystal so you can see the movement.
- Chronograph
- A watch with a stopwatch function, usually started and stopped with pushers beside the crown. Read more
- Chronometer
- A watch whose movement has passed a precision test, commonly COSC certification for Swiss watches (within 4 seconds slow and 6 fast per day).
- Complication
- Any function beyond hours, minutes and seconds, such as a date, chronograph or GMT. Read more
- COSC
- The Swiss official chronometer testing institute, which certifies movements to chronometer standards.
- Crown
- The knob used to wind the watch and set the time and date. Read more
- Crown guards
- Shoulders on the case that protect the crown from knocks.
- Crystal
- The transparent cover over the dial, usually sapphire, mineral glass or acrylic. Read more
- Cerakote
- A ceramic-based coating applied to a metal case or bracelet for added resistance to scratches, wear and corrosion.
- Date window
- An opening in the dial that shows the date from a rotating disc beneath it.
- Deployant clasp
- A folding clasp that keeps the strap or bracelet closed in a loop when opened. Read more
- Dial
- The face of the watch, carrying the markers, hands and printing.
- Dive extension
- A sliding or folding section in a clasp that lengthens a bracelet to fit over a wetsuit. Read more
- Eco-Drive
- Citizen’s name for its light-powered quartz movements. Read more
- End links
- The pieces that connect a bracelet to the case. Solid end links feel more substantial than folded ones.
- Escapement
- The mechanism that releases a mechanical movement’s energy in regular steps; it makes the ticking sound. Read more
- Exhibition caseback
- A transparent back, usually sapphire or mineral glass, that shows the movement.
- Field watch
- A simple, legible watch inspired by military issue watches, typically with Arabic numerals.
- FKM
- A fluoroelastomer rubber used for premium watch straps; durable and resistant to heat and dust. Read more
- GMT
- A function showing a second time zone, usually with a 24-hour hand and bezel. Read more
- Grey market
- New, genuine watches sold by retailers outside a brand’s authorised network, usually with a retailer warranty. Read more
- Hacking
- A feature that stops the seconds hand when the crown is pulled out, allowing precise time setting. Read more
- Hairspring
- The fine coiled spring attached to the balance wheel. Magnetism can make its coils stick together. Read more
- Hand-winding
- Winding a mechanical movement through the crown.
- Hardlex
- Seiko’s hardened mineral glass crystal. Read more
- Hesalite
- A name used for acrylic watch crystals; shatter-resistant and polishable. Read more
- Helium escape valve
- A valve on some dive watches that lets trapped gas out during decompression.
- Indices
- The markers on the dial that indicate the hours; also called hour markers.
- Integrated bracelet
- A bracelet designed to flow directly from the case with no conventional lugs. Read more
- ISO 6425
- The international standard for dive watches. Read more
- Jewels
- Synthetic rubies used as low-friction bearings in a mechanical movement. Read more
- Lug width
- The distance between the lugs, which determines strap width. Read more
- Lug-to-lug
- The length of a watch from the tip of the top lugs to the tip of the bottom lugs; key to fit. Read more
- Lugs
- The horns that extend from the case and hold the strap or bracelet.
- Lume
- Luminous material on hands and markers, such as Super-LumiNova, that glows after light exposure. Read more
- Mainspring
- The coiled spring that stores energy in a mechanical movement. Read more
- Manual
- A mechanical watch wound by hand through the crown rather than by a rotor. Read more
- Mecha-quartz
- A quartz movement with a mechanical chronograph module, such as the Seiko VK64. Read more
- Microbrand
- A small, usually independent watch company that sells direct to buyers. Read more
- Micro-adjust
- A clasp feature that lets you fine-tune bracelet length without removing links.
- Movement
- The internal mechanism that keeps time and powers the functions of a watch. Read more
- Moon phase
- A complication showing the phase of the moon through a window on the dial. Read more
- Miyota 9015
- A Citizen-made automatic movement with a 28,800 vph beat, hacking and hand-winding, known for a smooth sweep. Read more
- NATO strap
- A single strip of nylon that threads under the case and through both spring bars. Read more
- NH35
- A Seiko Instruments automatic movement used by many brands, with a 21,600 vph beat, hacking and hand-winding. Read more
- Patina
- The natural ageing of materials such as bronze or a dial’s lume over time. Read more
- Power reserve
- How long a fully wound mechanical watch runs without further winding. Read more
- PVD
- Physical vapour deposition, a thin hard coating used to colour steel cases and bracelets. Read more
- Perpetual calendar
- A calendar complication that accounts for month lengths and leap years automatically. Read more
- Pin and collar
- A bracelet link fastening where a tiny sleeve inside the link grips the pin; common on Seiko bracelets. Read more
- PT5000
- An automatic movement used by many microbrands, with a 28,800 vph beat and often described as a clone of the Sellita SW200-1. Read more
- Quartz
- A battery-powered movement regulated by a vibrating quartz crystal; very accurate. Read more
- Quick-release
- Spring bars with a small lever so a strap can be changed without tools. Read more
- Rotor
- The pivoting weight in an automatic movement that winds the mainspring. Read more
- Sapphire crystal
- A synthetic sapphire crystal; highly scratch-resistant. Read more
- Screw-down crown
- A crown that screws onto the case to improve water resistance. Read more
- Small seconds
- A seconds hand on a separate small sub-dial rather than at the centre.
- Spring bar
- The spring-loaded pin that holds a strap between the lugs.
- Sunray dial
- A dial finish with fine lines radiating from the centre that catch the light.
- Super-LumiNova
- A widely used photoluminescent lume pigment, in grades such as C3 and BGW9. Read more
- Swiss Made
- A legal label requiring a Swiss movement, Swiss casing and inspection, and a minimum share of costs in Switzerland. Read more
- Skeleton dial
- A dial with much of the movement cut away so it can be seen from the front.
- Slide-rule bezel
- A rotating bezel with calculation scales, found on some pilot chronographs. Read more
- Tachymeter
- A bezel or dial scale used with a chronograph to calculate speed over a known distance. Read more
- Tourbillon
- A rotating cage holding the escapement and balance, designed to average out positional errors. Read more
- Tritium
- A self-luminous material used in vintage paint and modern sealed gas tubes. Read more
- Unidirectional bezel
- A bezel that rotates one way only, so a knock can only shorten, never lengthen, a timed dive. Read more
- Vph
- Vibrations per hour; the beat rate of a mechanical movement, such as 21,600 or 28,800. Read more
- Water resistance
- A pressure rating, in metres, bar or ATM, describing how well a case keeps water out. Read more
- World timer
- A watch that shows many time zones at once on a city ring or disc. Read more
- Open-heart dial
- A dial with a window that shows part of the movement, usually the balance wheel.