Three numbers that tell the
health of a watch.

01 · The vital signsThree numbers, three stories.

When you place a mechanical watch on a timegrapher — be it a benchtop Witschi, a budget Weishi, or WatchScope on your smartphone — within seconds three numbers appear on the screen. Each tells a different story, and the three together say whether the watch is healthy or needs attention.

The daily rate (in s/d, seconds per day) tells you if the watch runs fast or slow. The amplitude (in degrees, °) measures how far the balance wheel swings on each oscillation — the "breath" of the movement. The beat error (in milliseconds, ms) measures how symmetric the tic-tac is, i.e. whether the two halves of each oscillation last the same time.

Seen separately these numbers feel abstract. Read with the right key, they become a diagnosis. In this guide we cover what each one measures, the healthy ranges, and when there's reason to worry.

02 · Daily rateWhat +5 s/d means.

Daily rate is the most immediate number: it tells how many seconds per day the watch gains (sign +) or loses (sign −) relative to astronomical time. A +5 s/d means after 24 hours the watch reads 5 seconds ahead of where it should. Over a full month, it gains two and a half minutes. On a human scale that's little; on the scale of fine watchmaking, it's a well-regulated movement.

The asymmetric COSC bracket (−4 to +6) is no accident: watchmaking prefers a watch that runs slightly fast over one that runs slow. At end of day, a fast watch keeps you on time; a slow one makes you late.

03 · AmplitudeThe breath of the balance wheel.

Amplitude is the angle the balance wheel sweeps on each oscillation, measured in degrees. It's the "breath" of the movement: a high value means the mainspring is transferring energy efficiently through the gear train to the balance wheel, the movement's regulating organ.

Typical amplitude for a healthy movement is between 220° and 330°. It drops with position (vertical has more pivot friction, so typically 30-50° lower than horizontal) and as the mainspring runs down during the day. Here are the key ranges:

04 · Beat errorThe limping tic-tac.

The balance wheel oscillates with two "half-beats": a tic and a tac. In a well-regulated movement, the two last exactly the same time. Beat error, expressed in milliseconds, measures the difference between them — the asymmetry of the beat, the tic-tac that limps slightly.

A high beat error doesn't significantly inflate the rate (the average evens out), but it wastes mainspring energy and makes the watch more vulnerable to shocks: with one half of the beat shorter than the other, a strong knock is enough to stop the movement. Here are the ranges:

Good news: a high beat error is often the easiest and fastest defect to correct. A competent watchmaker fixes it with a balance-and-pallet adjustment in minutes, without dismantling the whole movement. If beat error is the only out-of-spec parameter, a full service usually isn't needed.

05 · The complete pictureRead together, they tell the story.

Looked at one at a time, each of the three numbers tells only a fragment. It's reading them together that builds the diagnosis. Here are the most common scenarios and what they mean:

• All three in range (rate ±10 s/d · amplitude 250-310° · BE <1 ms): movement in full health. Keep wearing it, retest in 6-12 months.
• Only rate is off, amplitude and BE normal: only a regulator adjustment needed (the small "lever" on the hairspring). Few minutes in the workshop, low cost. Typical of a watch that has drifted 20-30 s/d after a few years.
• Low amplitude (under 220°), rate and BE normal: insufficient wind, or early wear signs. Keep the watch fully wound for a few days and retest; if it persists, book a service.
• Only beat error is high, rate and amplitude normal: balance adjustment, quick and cheap. See section 04.
• All three out of spec: the movement is past its service window. Dry lubricants, worn parts, possible magnetism. Book a full service.

WatchScope computes and displays the three values in real time from the phone's microphone, and interprets them automatically with a colour-coded verdict (green / yellow / red). It saves every test in the watch's history so you can see, year after year, how the movement behaves — and catch weak signals before they become problems.