A short lexicon of mechanical watchmaking
Terms as we use them across the journal — written for a reader with pliers on the table, not a textbook in hand.
The arc, measured in degrees, that the balance wheel swings through on each half-beat. A well-serviced movement usually reads somewhere between 220° and 300° dial-up, tapering somewhat when the watch is turned crown-down.
The difference in time between the "tick" and the "tock" of a healthy escapement, which should otherwise be perfectly even. Measured in milliseconds, and usually corrected by rotating the hairspring stud.
A balance spring's tendency to keep the same period of oscillation whether its swing is wide or narrow. No spring achieves this perfectly, which is part of why rate changes as a mainspring unwinds.
The spread in rate a movement shows when measured in different positions — dial up, dial down, crown up, crown down, and so on — caused mainly by gravity acting differently on the balance and its pivots.
The coiled ribbon of spring steel or alloy that stores energy when the watch is wound and releases it gradually through the gear train to keep the watch running.
The toothed drum that houses the mainspring, transmitting its torque to the gear train through the barrel's outer teeth as the spring unwinds.
The assembly — usually escape wheel plus pallet fork in a lever escapement — that converts the continuous rotation of the gear train into small, periodic impulses to the balance wheel.
The lever-shaped component that locks and releases the escape wheel in turn, passing a small push to the balance wheel with every swing and, in the process, giving the watch its audible tick.
The oscillating wheel, paired with the hairspring, that acts as the watch's timekeeping regulator — its steady back-and-forth swing divides time into equal beats.
A fine coiled spring attached to the balance staff that pulls the balance wheel back after each swing, setting the natural period of oscillation together with the balance's mass.
A small lever, usually carrying two pins, that changes the effective free length of the hairspring — and with it the watch's rate — without needing to touch the spring itself.
A design that regulates rate through small weighted screws or a variable-inertia rim on the balance itself, rather than through regulator pins — generally considered less prone to disturbance once set.
An instrument that listens to the escapement's ticking through a microphone and translates the pattern into rate, amplitude, and beat error — the main diagnostic tool at a home bench.
The angle, in degrees, that the balance wheel rotates while receiving its impulse from the pallet fork. A timegrapher needs this value entered correctly to calculate amplitude accurately.
A small synthetic ruby or sapphire bearing set into the plates or bridges, used at pivot points and impulse surfaces to reduce friction and wear compared with bare metal.
The small amount of intentional play a pivot has along its axis (endshake) and across it (sideshake) — too little causes friction and stopping, too much causes instability and noise.
The set of small levers and wheels behind the crown that let a single stem both wind the mainspring and, when pulled out, set the hands — named for replacing the separate winding key of pocket watches.
The length of time a movement will continue to run on a full wind before the mainspring's torque drops too low to maintain the balance's amplitude.
A small spring-loaded pawl (the click) that engages the teeth of the ratchet wheel, allowing the mainspring to be wound in one direction while preventing it from unwinding back through the crown.
The balance of mass around a balance wheel's axis. A wheel that is not poised runs faster or slower depending on which side faces up, contributing to positional error.