May 9, 2026 · 13 min read
How to Track Mechanical Watch Accuracy Over Time
A practical guide to measuring seconds-per-day, logging accuracy over time, and using that data to decide when to regulate or service a watch.
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Measuring accuracy is one of the most satisfying parts of watch ownership. Tracking seconds-per-day over time helps you decide whether a watch needs regulation or a service. This article explains practical measurement methods, how to log results, and how to interpret patterns.
Two measurement approaches
- Timegrapher: instantaneous rate, beat error, amplitude — great for diagnostics.
- Real-world rate: deviation over days or weeks — shows how the watch performs on the wrist.
How to measure seconds-per-day
Set the watch to a reference time (phone or atomic clock) at a known timestamp. After a fixed period — typically 24 hours, or several days for greater accuracy — compare the watch to the reference and compute deviation in seconds divided by days elapsed. Record the start and end timestamps and the calculated seconds-per-day in your log.
Logging methodology and consistency
Use the same measurement method and testing duration each time to keep results comparable. Note position (dial up, crown down), typical wear pattern, and whether you wore the watch actively or left it on a winder. Small differences in test conditions explain many apparent fluctuations.
Interpreting the numbers
- Stable within expected tolerance: no immediate action.
- Drifting gradually: consider regulation or a service if trend continues.
- Sudden large deviation: inspect for shock or moisture; visit a watchmaker.
Using the log to justify service
Bring your accuracy log to the watchmaker — it shows real-world performance and helps prioritize regulation versus a full service. If accuracy worsens after a service, log the post-service numbers to confirm the improvement.
Practical tips
- Measure over multiple days for increased accuracy.
- Record position and wearing habits.
- Log timegrapher outputs if available as attachments.
Conclusion
Tracking accuracy over time turns anecdote into evidence. A small, consistent log helps you maintain performance and provides useful data for watchmakers and resale.
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