Amplitude and What Changes It

Amplitude is the angular distance, in degrees, that the balance swings from its rest position to the extreme of each half-swing. A healthy lever watch typically shows amplitude somewhere in the range of roughly 220 to 310 degrees measured lying flat (dial up or dial down), with several tens of degrees lower typically expected once the watch is turned onto its edge, since gravity then loads the balance pivots differently. A timing machine derives amplitude acoustically from the timing of the tick relative to the tock, using the known geometry of the escapement, rather than by any direct optical measurement.

Because amplitude reflects how much energy actually reaches the balance on each impulse, it is sensitive to almost every source of friction and power loss in the watch, which is exactly why watchmakers treat it as the most diagnostically useful single number a timing machine produces. Low amplitude with an otherwise plausible rate points towards causes such as a weak or set mainspring, dried or contaminated lubricant anywhere in the train or escapement, bent or worn pivots increasing friction, a hairspring fouling on itself or on a neighbouring part, or magnetism affecting the hairspring's coils.

Excessive amplitude, though less commonly a complaint in itself, can indicate too little friction from severely under-lubricated or worn-smooth pivots, or a mainspring delivering unusually high torque, and matters because very high amplitude increases the risk of 'knocking' — the impulse jewel striking the back of the pallet fork's slot rather than passing cleanly through it — which is itself a further source of wear and rate disturbance.

Amplitude should always be read as a curve, not a single figure: across the mainspring's power reserve (amplitude typically declines gradually as the spring unwinds, with the decline being the diagnostically relevant feature rather than the peak figure alone) and across the six conventional testing positions, since a healthy escapement shows amplitude falling within a fairly narrow band across positions, while a movement with a specific mechanical fault often shows an amplitude drop concentrated in one or two positions.

Reading amplitude correctly therefore depends on comparing it against expectations for the specific calibre, across time and across position, rather than judging a single reading in isolation — which is why interpreting a timing machine printout is taught alongside, not instead of, understanding the mechanical causes that produce each pattern.