A mechanical watch that gains or loses a few seconds a day is normal. A watch that loses twenty is not. Here is where the real limits sit, what the certification standards actually require, and how to measure your own watch without a timing machine.
The short answer
A well-regulated automatic movement should run within −5 to +8 seconds per day in normal wear. Anything inside ±10 s/day is acceptable for a mass-produced calibre. Over ±20 s/day means the watch needs regulation or service.
What the standards require
There are three thresholds worth knowing, and they are not the same thing:
- Chronometer (COSC): −4 to +6 seconds per day for the movement alone, tested in five positions at three temperatures before it is cased.
- Swiss-made standards (ISO), which are looser: −10 to +30 s/day is legally permitted for “Swiss made” mechanical watches. That is a wide band, and most decent calibres sit well inside it.
- In-house tolerances: brands that regulate their own movements often publish −2/+2 (Rolex Superlative Chronometer) or 0/+5. These are cased-watch figures, not movement-only figures, so they are stricter in practice.
Why your watch behaves differently from the specification
Rate depends on position, temperature and state of wind. A watch lying dial-up on a nightstand runs at a different rate than one on a wrist at 30°C. That is why “six-position” testing exists: the movement is measured in dial-up, dial-down, crown-up, crown-down, crown-left and crown-right, and then averaged.
The three things that move your rate most:
- Amplitude. A freshly serviced movement runs at 280–310° amplitude. As lubrication degrades, amplitude drops and the watch slows, then becomes erratic.
- Magnetism. A single pass near a laptop speaker or a bag clasp can magnetise the hairspring and add 30 seconds a day. This is the most common cause of sudden rate changes and the easiest to fix.
- Wear pattern. If you take the watch off at 6pm and it sits dial-up for 14 hours, that position dominates the daily average.
How to measure your own watch properly
You do not need a timing machine to get a usable number. You need a reference clock and a week of patience:
- Synchronise your watch to a reliable reference — a phone clock synced to network time, or time.is — at a fixed hour, say 08:00.
- Wear it normally for 24 hours. Do not wind it by hand beyond what the rotor does.
- At the same hour the next day, note the difference in seconds.
- Repeat for five to seven days and average. A single day is noise; a week is a rate.
Record the average and the spread. A watch running +3 s/day with a spread of ±2 is healthy. A watch averaging +2 but swinging between −15 and +20 has an amplitude or lubrication problem, not a regulation problem.
When to have it regulated
Regulate when the average drifts outside ±10 s/day and the watch has been demagnetised. A regulation is a five-minute job on a timing machine: the regulator arm is nudged and the watch is re-measured. A service is a different matter — that is when amplitude is low, the watch stops overnight, or the rate is erratic rather than simply offset.
What we do before shipping
Every watch we send is timed in six positions on a timing machine, regulated, then worn on a bench movement for 72 hours to confirm the rate holds under a real power curve. We send the timing printout with the order. If your watch arrives outside ±8 s/day, tell us and we will take it back and re-regulate it.