Mechanical watch timing, explained
Last updated 23 June 2026
If you have ever wondered what a timegrapher actually measures — or whether the iPhone in your pocket can do the same job — this is the plain-English version. Below: what each reading means, and the healthy ranges watchmakers look for.
What is a timegrapher?
A timegrapher is an instrument that measures how accurately a mechanical watch keeps time by listening to the sounds its movement makes.
Every mechanical watch has an escapement that ticks at a steady rhythm — typically six to ten times per second. Each tick is a tiny mechanical impulse with a characteristic sound. A timegrapher captures those sounds, measures the precise interval between them, and converts that timing into three core readings: rate, beat error, and amplitude. Watchmakers use it to diagnose a movement, regulate it, and confirm a service was successful. Traditional bench timegraphers (such as those made by Witschi) clamp the watch into a microphone holder; the underlying principle is pure signal processing on the tick sounds.
Can an iPhone be a timegrapher?
Yes. Because a timegrapher is fundamentally a microphone plus signal processing, a modern smartphone has everything required.
The iPhone microphone picks up the tick and tock impulses, and a digital signal processing (DSP) core measures the intervals between them — exactly as a bench unit does. Oscillo uses this approach to compute rate, beat error, and amplitude in real time, and adds a live timing diagram that plots every beat as it lands. The main difference from a professional bench is sensitivity to ambient noise: the tick of a movement is very quiet, so readings are most reliable in a quiet room with the bottom of the phone (where the microphone sits) resting against the watch crystal. In those conditions the results are comparable to what a watchmaker sees on the bench. See the accuracy FAQ for how a bench snapshot relates to real-world wrist performance.
The core readings
Rate is the headline accuracy figure: how many seconds per day the watch gains (shown as a positive number, e.g. +3 s/d) or loses (negative, e.g. −5 s/d). A timegrapher derives it from the average interval between ticks compared to the movement's nominal frequency. Rate is measured in a single position over a short window, so it is a snapshot — the same movement can show a different rate dial-up versus crown-down.
Beat error is the timing difference between the "tick" and the "tock" — the two half-swings of the balance wheel. Ideally the two halves are perfectly symmetrical and the beat error is zero. In practice, under 0.5 ms is excellent and most healthy movements stay under about 1.0 ms. Beat error does not directly add seconds per day, but a large value reduces the balance wheel's ability to self-correct and makes the rate more sensitive to position and shock. It is corrected by adjusting the hairspring collet.
Amplitude is how far the balance wheel rotates on each swing, measured in degrees. It is the single best indicator of a movement's mechanical health. A healthy movement typically shows 250°–310° when fully wound in the dial-up position.
| Amplitude | What it usually means |
|---|---|
| 250°–310° | Healthy — typical for a well-serviced movement |
| below ~200° | Low — possible worn mainspring, dried lubricants, or a dirty movement; rate becomes less stable |
| above ~320° | Risk of rebanking ("knocking"), where the impulse pin overswings and contacts the wrong side of the pallet fork, causing erratic timekeeping |
Amplitude naturally falls as the mainspring unwinds through the day, so it is always quoted alongside the state of wind and position.
BPH (beats per hour) is the movement's oscillation frequency — how many times the escapement ticks each hour. The timegrapher needs to know it to interpret the signal correctly. Common values:
| BPH | Frequency | Beats / second |
|---|---|---|
| 18,000 | 2.5 Hz | 5 |
| 21,600 | 3 Hz | 6 |
| 28,800 | 4 Hz | 8 |
| 36,000 | 5 Hz | 10 |
28,800 BPH is the most common modern rate. A higher beat rate generally makes a watch more resistant to positional disturbance.
Lift angle is the angle through which the escape lever pushes the balance during the impulse. It is a fixed property of a given movement (commonly around 52°) and is not something the watch's accuracy depends on — but a timegrapher must be told the correct lift angle to calculate amplitude from the tick sounds. An incorrect lift angle leaves rate and beat error unaffected but throws off the amplitude reading. The figure is published in movement specifications and watchmaker references.
What is a good rate for a mechanical watch?
It depends on the standard the watch is built to. A typical everyday automatic that stays within roughly ±10 seconds per day is doing well; many enthusiasts consider anything inside ±5 s/d excellent. Certified watches are held to tighter, published tolerances:
| Standard | Daily rate tolerance |
|---|---|
| COSC chronometer | −4 / +6 s/d |
| METAS Master Chronometer | 0 / +5 s/d |
| Typical good automatic | about ±10 s/d |
Note: these are bench tolerances measured across positions. What your watch does on your wrist over a real day can differ — which is why Oscillo pairs the Timegrapher with a Precision Log that measures observed rate over days of wear.
Why the bench reading and the wrist differ
A timegrapher reading is a short measurement in one fixed position. On the wrist, a watch constantly changes position, warms to body temperature, and runs through its power reserve — all of which shift the effective rate. That is normal, not a fault. The full explanation, including positional variation, mainspring tension, temperature, and magnetism, is in the mechanical watch accuracy FAQ.