Synchronize your watch

  • There are two parts to this process
    • You need a running watch you want to measure the accuracy of
    • You also need a trusted time source to measure your watch against

The watch I'll leave to you. For a trusted time source, I use the NIST time widget. You also can use a cell phone, GPS, or computer connected to an internet time source

Here is the NIST time widget. You can also use the pnline NIST time page:

  • Sync Minute and Second Hands
    • When the second hand reaches 0 (the 12 o'clock position), set the minute hand to exactly the minute, or 5 minute, or 15 minute index. If your watch doesn't have 60 minute divisions, this may take a few minutes.
  • Record TIme Offset
    • When the second hand reaches the 0 position, look at the time widget, and note the reference time and watch time. Subtract the two, and you have the difference. If your watch only has divisions every 5 minutes, you'll need to wait until the minute hand lines up on the next 5 minute marker.
    • - If the offset is over 30 seconds, next time watch second hand reaches 0, reset the watch to the minute closest to the time on the time source and record the adjusted difference.
  • Calculate drift per day
    • Take the two most recent measurements, and calculate the number of days between them. Divide the total drift by the number of days to get drift per day.
  • Keep track of your measurements
    • Record the date, time and offset from your trusted time source
    • Check the time again tomorrow, next week or next month. Check it often.
    • Keep track of the measurements, you can graph them using excel or other charting tool
    • Track the accuracy of your watches over time. If a watch becomes less accurate, it needs to be serviced by a competent watchmaker
    • Make sure you have every watch serviced by a competent watchmaker every 5 years
    • Most quartz watches are accurate to a few seconds a month.
    • A good mechanical watch will be accurate to around 10 seconds a day, or about a minute a week.
    • A chronometer has formal specifications it must meet:
COSC Standards
Mechanical Quartz
Average daily rate: -4/+6 Average daily rate at 23C: plus/minus 0.07
Mean variation in rates: 2 Rate at 8C: plus/minus 0.2
Greatest variation in rates: 5 Rate at 38C: plus/minus 0.2
Difference between rates in H & V positions: -6/+8 Rate stability: 0.05
Largest variation in rates: 10 Dynamic rate: plus/minus 0.05
Thermal variation: plus/minus 0.6 Temporary effect of mechanical shocks: plus/minus 0.05
Rate resumption: plus/minus 5 Rate resumption: plus/minus 0.05
n/a Residual effect of mechanical shocks: plus/minus 0.05;

200 shocks equivalent to 100 G (981 m/sec**2, 3,217 ft/sec**2)