Mechanical Watch Accuracy: A Simple Seven-Day Log
An editorial guide based on published technical references. Manufacturer examples describe the genuine models in those references; their specifications and certifications do not establish the performance of products listed in this catalog.
A single reading shows whether a watch is ahead or behind, but gives little context. A consistent log is more useful when comparing your experience with the stated specification.
Why the result changes
Grand Seiko explains that mechanical rate varies with winding state, temperature and resting position. Its manual recommends observing daily results over a week to ten days and distinguishes controlled laboratory measurements from accuracy during wear. Read the manufacturer’s explanation.
Use one reference throughout
Our suggested worksheet has five columns: date, observation time, signed offset in seconds, wearing hours and overnight position. Check against the same reference at approximately the same time. Record “+” for ahead and “−” for behind. Note any time you reset the hands, because that starts a new measurement interval.
A worked example
| Observation | Total offset |
|---|---|
| Start | 0 seconds |
| After 24 hours | +6 seconds |
| After 48 hours | +11 seconds |
| After 72 hours | +18 seconds |
In this invented example, the average is 18 ÷ 3 = +6 seconds per day. Do not add the accumulated offsets together; each already includes earlier gain. The daily changes are +6, +5 and +7 seconds.
Compare like with like
Send the log and the exact movement specification when asking about an unexpected result. A tolerance published for a different calibre is not an acceptance limit for yours. Ask which specification applies and what inspection would resolve the discrepancy.
Sources & further reading
References checked on October 17, 2026. This is a research guide, not a hands-on product test.