Amplitude
The angle through which a balance wheel swings from its resting position, often used by watchmakers when assessing a mechanical movement.
The language of horology
Watchmaking glossary.
Clear definitions for the terms that appear in catalogs, conversations and watchmaker's benches.
Annual calendar
A calendar complication that accounts for 30- and 31-day months but usually needs correction once a year after February.
Automatic movement
A mechanical movement whose mainspring is wound by a rotor responding to the movement of the wearer's wrist.
Balance wheel
The oscillating component in many mechanical watches that works with a hairspring to regulate the escapement.
Bezel
The ring surrounding a watch crystal. It may be fixed or rotating and can carry a timing, tachymeter or other scale.
Caliber
A name or reference for a specific watch movement design or family; the term alone does not establish quality or origin.
Chronograph
A watch function that measures elapsed time independently of the ordinary time display.
Chronometer
A precision timekeeping instrument that has passed a defined certification test, such as the applicable COSC program.
Complication
Any watch function beyond the basic display of hours, minutes and seconds; common examples include date, chronograph and moon phase.
COSC
Contrôle Officiel Suisse des Chronomètres, the Swiss institution that tests and certifies chronometers under defined criteria.
Escapement
The mechanism that meters energy from a watch's gear train to its oscillator in controlled increments.
Flyback chronograph
A chronograph that can reset and restart timing with a single action, useful for measuring successive intervals.
GMT
A common label for a watch displaying a second time zone, often with an extra 24-hour hand; setting behavior varies by movement.
Hairspring
A fine spring attached to a balance wheel that helps regulate its oscillation in a mechanical watch.
In-house movement
A broad industry phrase for a movement developed or made within a brand's organization; usage varies and is not a standalone quality test.
Lug-to-lug
The distance from the end of one watch lug to the opposite lug, a useful measure of how a case spans the wrist.
Mainspring
The coiled spring that stores energy in a mechanical watch movement.
Master Chronometer
A designation used for watches meeting a specific certification program; check the exact program, tests and model scope.
Perpetual calendar
A calendar mechanism designed to account for varying month lengths and the leap-year cycle within its calendar system.
Power reserve
The approximate running time a fully wound watch can operate before its stored energy is exhausted.
Rattrapante
A split-seconds chronograph with an additional hand that can stop to record an intermediate time while the main hand continues.
Rotor
A weighted, pivoting component that winds an automatic watch's mainspring as the watch moves.
Spring Drive
A Seiko-developed system in which a mainspring drives the gear train and an electronic regulator controls its rate.
Tachymeter
A scale, often on a chronograph bezel, used to calculate average speed over a measured distance.
Tourbillon
A rotating carriage that carries parts of a mechanical watch's regulating system; historically developed to address positional effects.
Unidirectional bezel
A rotating bezel that turns in one direction, commonly used to track elapsed time on a dive watch.
Water resistance
A tested property of a watch case and its seals; the marked rating is not a universal guarantee for every real-world activity.