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.
Manufacture standard
Rolex Superlative, Patek Philippe Seal, Grand Seiko Special: in-house post-COSC regulations, tighter still.
±2 s/dCOSC-certified chronometer
The Swiss ISO 3159 standard, applied to mechanical movements by Rolex, Omega, Breitling and similar.
−4 to +6 s/dWell-regulated movement
Normal range for a quality non-certified mechanical watch. Covers most ETA, Sellita, Miyota movements in good health.
±15 s/dRegulation or service
The rate is too far off to ignore: the movement either needs regulation (a few minutes) or a full service if accompanied by low amplitude.
< −20 or > +30 s/dThe 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.
Rate changes with the position of the watch (horizontal vs vertical) and with the state of wind (mainspring full vs depleted). For a reliable reading, always test wrist-worn or in the same position, with the spring near full wind.
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:
Excellent health
Fully wound, horizontal. The movement is transferring energy at peak efficiency. Typical range for a watch just out of service.
270° – 310°Ideal COSC range
The accepted standard for COSC certification: the movement has enough "breath" to maintain a stable rate across all positions.
250° – 290°Acceptable
Borderline range. Can be normal in vertical or at partial wind, but if it persists wrist-worn / horizontal it signals early wear.
200° – 250°Service required
The movement no longer has enough energy: dry lubricants, worn parts, magnetism, or damaged hairspring. Workshop.
< 200°Amplitude over 330° with a fully wound watch is just as problematic: it's called knocking or over-swing. The balance wheel hits the pallet fork on every oscillation, damaging it over time. Rare, but if the app flags it, take the watch to a workshop.
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:
Excellent
Professional regulation, inaudible. Typical of a movement just back from a master watchmaker's overhaul.
< 0.5 msAcceptable
Factory tolerance for most quality watches. The tic-tac is nearly symmetric, undetectable by ear.
0.5 – 1.0 msNeeds adjustment
Requires a small balance wheel adjustment — a few minutes in the workshop, low cost. Not a full service, just a calibration.
1.0 – 1.5 msProblem
The movement stops easily under shock and wastes wind. Service or structural regulation recommended.
> 1.5 msGood 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.
Reading the data: rate, amplitude and beat error explained
What is beat error in a watch and what value is good?
Beat error is the timing gap between the tick and the tock, measured in milliseconds. In an ideal movement the two half-swings of the balance wheel are perfectly symmetric, so the value is near zero. Below 0.5 ms is excellent and under about 1.0 ms is still acceptable; higher figures mean the balance and hairspring are out of alignment and a watchmaker should re-center the impulse pin.
What is balance wheel amplitude and what is a healthy value?
Amplitude is the angle the balance wheel swings through on each oscillation, measured in degrees. It is the clearest sign of how much energy the escapement is delivering and therefore of the movement's overall health. Dial-up and fully wound, a value of about 270 to 310 degrees is healthy; readings that drop below roughly 200 degrees point to tired oil, friction or a movement that needs a service.
What is an acceptable rate for a mechanical watch?
Rate tells how many seconds per day the watch gains or loses, so the ideal is as close to zero as possible. A certified chronometer must stay within the COSC window of −4 to +6 s/d. For a good mechanical watch that is not chronometer-certified, anything within roughly plus or minus 10 to 15 s/d is perfectly normal and easy to live with day to day.
What do the numbers on a timegrapher actually mean?
A timegrapher returns three core figures that together describe the watch. Rate, in s/d, says how far ahead or behind the watch runs each day, so it measures accuracy. Amplitude, in degrees, says how widely the balance wheel swings, so it measures energy and overall health. Beat error, in milliseconds, says whether the tick and the tock are evenly spaced, so it measures the symmetry of the escapement.
How does WatchScope measure rate, amplitude and beat error?
WatchScope uses the smartphone microphone to capture the sound the escapement makes at every beat of the balance wheel. A digital signal processing engine isolates those tiny ticks from background noise and analyses their exact timing in real time. From that stream it derives rate, amplitude and beat error and shows them live on screen, turning the phone into a working timegrapher without any extra hardware.
Read your watch's
heartbeat.
WatchScope is free on Android. Rate, amplitude, beat error in real time from your phone's microphone. 30 seconds for the first test.