The accuracy of mechanical watches varies slightly from day to day, depending on various conditions. Therefore, the loss / gain of mechanical watches is not measured by a daily rate, but by an average daily rate over a period of 7 to 10 days. For this reason, the accuracy of mechanical watches is indicated by "the mean daily rate."
The accuracy of the mechanical watch in use
The accuracy of a mechanical watch varies slightly depending on individual user conditions such as winding state of the mainspring due to movement of the users’ arm, ambient temperature, and posture (direction of the watch). Accordingly, actual accuracy of a watch in use may differ from specifications in the "Grand Seiko Standard."
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.
The accuracy of the mechanical watch movement at rest
To establish a benchmark accuracy of a mechanical watch which does not depend on usage environment, loss / gain of a mechanical watch is measured before the movement is assembled in the case. The accuracy of the movement is measured under controlled conditions over a certain number of days, and the result is called "the accuracy of a mechanical watch movement at rest."
The measurement result for each watch is written in the "Grand Seiko Standard Inspection Certificate," which is provided with the watch by the retailer at time of purchase. This result is an average loss / gain of time over a 17 day period, which was measured in the factory where the temperature and position of the movement are controlled in accordance with the "Grand Seiko Standard."