A timegrapher listens to a mechanical watch's escapement, the part that ticks, and works out how the movement is running. It takes under a minute and nothing has to be opened.
The three numbers
| Number | What it measures | Healthy range |
|---|---|---|
| Rate | Seconds gained (+) or lost (−) per day | −4 to +6 s/d for a COSC chronometer |
| Amplitude | How far the balance wheel swings | 250 to 310° for a fully wound watch |
| Beat error | The asymmetry between tick and tock | Under 0.5 ms is excellent; above 1.5 ms suggests regulation |
Reading the trace
Every dot on the trace is a beat. A line that climbs means the watch is gaining; one that falls means it's losing. Two lines apart instead of one show beat error. In Horology, gold dots are ticks and green dots are tocks.
Getting a good reading
- Wind the watch fully.
- Find a quiet room.
- Press the bottom of your iPhone firmly against the case, near the crown, and keep still.
In Horology, the microphone is only used while measuring, and the audio is analysed on your iPhone and never recorded or uploaded.
To see how evenly a movement keeps time in different orientations, run a six-position test.