A useful timing log records how a watch’s difference from a reference changes over time. A reading of twenty seconds fast describes its current offset; a starting reading and a known interval turn that observation into a rate. Keep both the raw readings and the calculation.
Record the starting difference
Choose a reliable time reference with a seconds display and use the same reference throughout. Note the date, observation time and watch’s offset: use a plus sign when it is ahead and a minus sign when it is behind. You do not need to start at exactly zero.
Read the watch consistently rather than claiming more precision than its display allows. Repeat at roughly the same time each day, recording the actual observation time. If you reset the hands, change the displayed time zone or the watch stops, mark that event and begin a new continuous segment.
Calculate change over elapsed time
Subtract the starting offset from the ending offset, then divide by elapsed time in days. For example, a watch that begins eight seconds ahead and is twenty seconds ahead exactly seventy-two hours later has gained twelve seconds over three days: (20 − 8) ÷ 3 = +4 seconds per day.
This is an illustrative calculation, not a test result. For an interval shorter or longer than a whole number of days, divide the elapsed hours by twenty-four first. Averaging the offsets themselves would not give the rate. Retain individual readings so a sudden change remains visible.
Keep the wearing conditions visible
Seiko’s mechanical-watch guidance identifies winding state, arm movement, temperature and resting position as factors affecting timekeeping. Alongside each reading, note approximate wearing hours, winding and how the watch rested overnight. Follow the actual model’s winding instructions.
Keep your ordinary routine reasonably consistent during the record. If you change something, write it down rather than silently combining different conditions. Our between-wears storage guide covers the wider arrangement when the watch is off your wrist.
Compare with the right specification
The Grand Seiko 9S instructions recommend assessing average daily gain or loss over seven to ten days. They also distinguish controlled movement testing from accuracy during normal wear. Use your own watch’s specification and assessment conditions; a home log does not reproduce a certification test.
If an unexplained change persists, share the readings and routine with a watchmaker. The figures alone cannot identify its cause: our magnetism guide explains one possible influence. Browse Watches & Wear for more practical ownership guides.
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