Why doesn’t the accuracy of my Grand Seiko mechanical watch match the rate written on the Grand Seiko Standard Inspection Certificate?

The accuracy written on the Grand Seiko Standard Inspection Certificate is the accuracy of the Grand Seiko mechanical watch movement at rest, which is measured before the inside movement of the watch is assembled in the case. Since the accuracy of a mechanical watch varies slightly depending on individual user conditions, the actual accuracy during use may differ from the numerical value specified in the certificate. The accuracy is affected by conditions such as winding state of the mainspring due to movement of the users’ arm, ambient temperature, and posture (direction of the watch).


The target accuracy range of Grand Seiko mechanical watches in use is -1 to +10 seconds per day. To determine accuracy in use, measure loss / gain under normal use conditions for approximately 7 to 10 days and calculate the average loss / gain per day.