Beat Error
Beat error is the small timing difference between the two swing directions of the balance wheel, measured in milliseconds on a timing machine. A low figure means an even rate, while a high one can be reduced during regulation by resetting the balance's rest position.
At a glance
- Unit
- Milliseconds (ms)
- Ideal value
- Close to 0.0 ms
- How it is measured
- On a timing machine
A mechanical heart ticks several times a second: the balance wheel swings one way, then back the other. Ideally those two half-swings take exactly the same time. Beat error measures the small imbalance between them, usually expressed as a number from 0.0 to a few milliseconds.
What the number tells you
The closer the figure sits to zero, the more symmetrically the balance wheel is ticking. In practice you watch for:
- Low beat error: an even rate and a more stable amplitude
- High beat error: the balance rests off center, and a sharp knock can make the watch stop
Why it matters
A high beat error does not by itself make a watch run fast or slow, but it makes the rate uneven and can pull amplitude down. The good news is that it is a fault a watchmaker can correct. By rotating the hairspring collet on the balance staff, or moving the stud carrier on modern movements, the watchmaker resets the balance's rest position so the impulse pin sits midway between the banking pins and the two swings even out. That work is usually done in the same session as regulation and a beat rate check.
For what that kind of upkeep involves, see my guide to caring for a mechanical watch.
Examples
If a timing machine reads 0.2 ms of beat error, the two swings are nearly equal and the rate is considered even. A high figure like 4 ms is a signal for the watchmaker to correct during regulation.
On an accessible automatic such as the Seiko 5 Sports, a low beat error helps keep the daily rate even and more predictable.
View this watch
Comparison
Beat error and daily rate measure different things and are often confused.
| Option A | Option B | Notes |
|---|---|---|
| Beat error | Daily rate | Beat error shows the imbalance between the two swing directions; daily rate shows how many seconds the watch gains or loses over 24 hours. A low beat error does not automatically mean zero drift. |
Related terms
Watches that show this
Frequently asked questions
What is a good beat error value?
The closer to zero, the better. The general aim is to get the figure as near to zero milliseconds as possible; higher values reaching several milliseconds make the rate uneven and are best corrected during regulation.
Can a high beat error be corrected?
Yes. A watchmaker rotates the hairspring collet on the balance staff, or moves the stud carrier on modern movements, to reset the balance's rest position, even out the two swings and bring the beat error down. It is a routine adjustment, usually done in the same session as regulation and a beat rate check.
How does beat error affect a watch's accuracy?
Beat error alone does not make a watch run fast or slow, but it makes the rate uneven and can lower amplitude. At high values the watch may stop after a sharp knock, which is why a low figure is preferred for an even rate.