Watch Glossary
The complete A–Z of horological terminology. Whether you're a beginner or seasoned collector, this glossary explains every essential watch term.
A
3 terms
- Automatic Movement
- A self-winding mechanical movement powered by a rotor that spins from the natural motion of your wrist. No battery required.
- Antimagnetic
- A watch with shielding to protect the movement from magnetic fields. ISO 764 certifies resistance to 4,800 A/m; some specialised watches resist up to 80,000 A/m.
- Aperture
- A small window cut into the dial, typically displaying the date, day, or moon phase.
B
2 terms
- Bezel
- The ring surrounding the watch crystal. Can be fixed, rotating (uni- or bidirectional), or feature scales like tachymeter or GMT.
- Bracelet
- A metal band attached to the watch case, typically composed of links. Common types: Oyster, Jubilee, President, Milanese.
C
6 terms
- Calibre
- The reference number identifying a specific watch movement (e.g. Rolex Cal. 3235, Omega Cal. 8800).
- Chronograph
- A watch with stopwatch functionality, typically using pushers at 2 and 4 o'clock to start, stop, and reset elapsed time.
- Chronometer
- A precision watch certified by an independent body (most commonly COSC) to specified accuracy standards.
- Complication
- Any watch function beyond basic timekeeping — date, GMT, chronograph, moonphase, perpetual calendar, etc.
- COSC
- Contrôle Officiel Suisse des Chronomètres — the Swiss agency that certifies watch accuracy. Standards: -4/+6 sec/day for mechanical watches.
- Crown
- The knob on the side of the case used to set time, date, and wind the movement.
D
2 terms
- Date Window
- An aperture on the dial showing the current date.
- Deployant Clasp
- A folding bracelet/strap clasp that opens to fit over the hand, then folds closed.
E
2 terms
- Escapement
- The heart of a mechanical watch — it regulates the release of energy from the mainspring to the gear train.
- ETA
- Swiss movement manufacturer (owned by the Swatch Group) supplying calibres to many watchmakers.
G
2 terms
- GMT
- Greenwich Mean Time. A watch complication displaying a second time zone, typically with a 24-hour hand and bezel.
- Glycine
- (See also Hour Markers, Indices.) The dial elements indicating hours.
H
2 terms
- Hacking
- A feature that stops the seconds hand when the crown is pulled out, allowing precise time setting.
- Helium Escape Valve
- A valve on professional dive watches that releases helium during decompression to prevent crystal damage.
I
2 terms
- In-house Movement
- A movement designed and manufactured entirely by the watch brand itself (vs. sourced from ETA, Sellita, etc.).
- ISO 6425
- The international standard certifying genuine dive watches. Requires 100m+ water resistance, screw-down crown, and shock resistance.
L
2 terms
- Lugs
- The case extensions where the strap or bracelet attaches.
- Lume
- Luminous material on hands and indices for low-light visibility. Modern lumes include Super-LumiNova and Chromalight.
M
3 terms
- Manual Wind
- A mechanical movement that must be wound by hand via the crown. Typical reserve: 36-72 hours.
- METAS
- Swiss Federal Institute of Metrology. Their Master Chronometer certification exceeds COSC standards (-0/+5 sec/day).
- Moonphase
- A complication displaying the current phase of the moon, traditionally on a small aperture.
P
3 terms
- Perpetual Calendar
- A complication that displays date, day, month, and leap year — correctly accounting for varying month lengths.
- Power Reserve
- How long a fully wound movement will run without further winding (typical 38-80 hours).
- Pushers
- Buttons on the case (usually for chronograph operation) to start, stop, and reset functions.
Q
1 term
- Quartz Movement
- An electronic movement powered by a battery, regulated by a vibrating quartz crystal. Accurate to ±15 seconds/month.
R
2 terms
- Reference Number
- A unique identifier for a specific watch model (e.g. Rolex 126610LN, Omega 310.30.42.50.01.001).
- Rotor
- The semi-circular weight in automatic watches that swings with wrist movement to wind the mainspring.
S
4 terms
- Sapphire Crystal
- A synthetic sapphire watch crystal — among the hardest materials used in watchmaking, second only to diamond.
- Screw-Down Crown
- A crown that screws into the case to enhance water resistance. Essential for dive watches.
- Solar Movement
- A quartz movement powered by a solar cell (e.g. Citizen Eco-Drive, Seiko Solar).
- Sub-Dial
- A smaller dial within the main dial, used for chronograph counters, small seconds, day/date, etc.
T
3 terms
- Tachymeter
- A bezel scale used to measure speed based on travel time over a known distance.
- Tourbillon
- A complex mechanism that rotates the escapement to counteract gravity's effect on accuracy. Historically a status symbol.
- Tritium
- A radioactive luminous material used in vintage and military watches. Older tritium dials develop "patina" over time.
U
1 term
- Unidirectional Bezel
- A rotating bezel that only turns counter-clockwise — used on dive watches to prevent accidentally extending the indicated dive time.
V
1 term
- Vibrations Per Hour (VPH)
- The frequency of the balance wheel. Higher VPH (28,800+) = smoother seconds hand and finer time precision.
W
1 term
- Water Resistance
- A watch's ability to resist water ingress. Stated in metres or ATM (1 ATM = 10m static pressure).