Amplitude
The arc through which the balance wheel swings — a key indicator of how well the movement is running.
What is Amplitude?
Amplitude is the measurement of how far the balance wheel swings in degrees during each oscillation. A full rotation is 360°; a healthy mechanical watch balance wheel typically swings between 270° and 315° in each direction when measured on a timing machine with the watch in the dial-up position.
What Amplitude Tells Us
Amplitude is one of the most useful diagnostic readings a watchmaker takes:
- High amplitude (280–315°) — the movement is well-lubricated, the mainspring is in good condition, and the power delivery through the gear train is efficient. This is the target range.
- Low amplitude (under 220°) — something is consuming energy it shouldn't be: dried or congealed lubricant causing friction, a weak or set mainspring, a worn pivot, or a problem in the gear train. Low amplitude is a reliable sign that a service is overdue.
- Very high amplitude (over 330°) — rare, and usually only an issue in freshly wound or recently serviced movements; can cause the balance wheel to "bank" (over-swing and contact the pallet fork incorrectly).
Amplitude and Servicing
A before-and-after amplitude reading is one of the clearest ways to demonstrate the benefit of a service. It is common to see amplitude rise by 40–80 degrees after cleaning, fresh lubrication, and a new mainspring — translating directly into improved accuracy and power reserve.