Watchmaking glossary
Plain-English definitions for the terms you'll run into on the bench, in the forums, or on a movement spec sheet.
- Amplitude
- The angle the balance wheel swings through on each oscillation, measured in degrees — a key health check on a timegrapher.
- Automatic (Self-Winding)
- A mechanical movement wound by an internal rotor that spins with wrist motion, topping up the mainspring without a manual crown wind.
- Beat Error
- The difference in timing between a watch's tick and tock — ideally close to zero for even amplitude in both directions.
- Bezel
- The ring surrounding the crystal — can be fixed, rotating, or used to time an elapsed interval.
- Calibre
- The model or reference number of a movement, identifying its size, layout and specification.
- Chronometer
- A watch whose movement has been independently tested and certified for accuracy, most commonly by COSC in Switzerland.
- Complication
- Any function beyond basic timekeeping — a date, chronograph, GMT or moonphase display, for example.
- Escapement
- The mechanism that regulates and releases the mainspring's energy in small, precise increments — the source of a watch's tick.
- Gasket
- A rubber or silicone seal — at the crown, caseback or crystal — that keeps a watch water and dust resistant.
- Jewel
- A synthetic ruby (or sapphire) bearing used at friction points in a movement to reduce wear and improve accuracy.
- Ligne
- The traditional French unit for movement diameter, equal to roughly 2.2558mm — still the standard sizing unit in watchmaking.
- Lug Width
- A case's lug-to-lug gap in millimetres — determines which strap or bracelet widths will fit.
- Mainspring
- The coiled spring that stores the energy which powers a mechanical movement.
- Power Reserve
- How long a fully wound mechanical watch keeps running before it needs winding again.
- Quickset
- A date mechanism that can be advanced directly via the crown, rather than only by cycling the hands through midnight.
- Rotor
- The weighted, semicircular arm in an automatic movement that winds the mainspring as it swings with wrist motion.
- Tourbillon
- A rotating cage holding the escapement, designed to average out timekeeping errors caused by gravity in different positions.
- Water Resistance (ATM / Bar)
- A rating of a watch's sealing against water under static pressure — 1 ATM/bar is roughly 10 metres, though it isn't a literal depth guarantee.