How to keep a meaningful mechanical-watch accuracy log

Distinguish accumulated deviation from a daily rate and from an instrument's instantaneous reading. Power, temperature, position and measurement method can all influence a single observation.

Accumulated error is not daily error

A watch twenty seconds ahead has not necessarily gained twenty seconds each day. Measure the change between two observations and account for the elapsed time. Use a consistent reference and avoid extrapolating a few minutes of observation into an apparently precise daily figure.

Keep wearing conditions comparable

Daily wear and overnight resting positions can produce different cumulative results. Record winding, wearing duration and resting position across several days. Repeatedly changing all the conditions makes two readings difficult to compare.

What a timing instrument can show

A timegrapher observes particular operating conditions; settings, signal quality and movement type affect its display. One position is not a substitute for multiple positions, power levels and real wearing observations. Certification also distinguishes movement and complete-watch requirements and different categories.

Common misunderstandings

Do not repeatedly adjust the regulator because of one day's result. A stable bias differs from a sudden large change. If the behaviour changes abruptly or includes stopping or unusual sounds, record the circumstances and investigate the cause.

Your practical checklist

• Keep several consecutive observations with one reference.
• Calculate the new deviation, not just the accumulated number.
• Record conditions surrounding any sudden change.