The beautiful spiral shape of the balance spring is deceptively simple. Its performance depends on the most minute and delicate adjustments. Imagine this: while the thickness of the spring is much less than one tenths of one millimeter in diameter, the craftsman can see differences of 1/1000th of a millimeter in the way the spring is wound. The craftsmen and women to whom this task is entrusted make the necessary adjustments by eye, and with nothing more high tech than a pair of specially designed tweezers!

Grand Seiko's certification inspection process for the mechanical caliber 9S series takes 17 days. The movement is placed in six positions and is tested at three different temperatures, and its daily variations must fit within the very strict tolerance rates.

The Grand Seiko standard differs from the other recognised chronometer standards in two important respects. The Grand Seiko standards tests each watch in six positions, rather than five and at three temperatures rather than two. Why? Because the Grand Seiko tests seek to replicate what happens in real life. The sixth position is the position many people leave their watch when not worn, namely with the 12 o’clock position up right, and the extra temperature rating is closer to the body temperature. The idea is simple; to test the watch under the conditions similar to the actual usage.

Remarks :
Grand Seiko certification is made to the movement before casing. The movement performance is carefully measured in the static position under the artificially controlled condition.

The accuracy of the watch may vary depending on the actual usage conditions and may be different from the certified accuracy.

The actual Grand Seiko’s accuracy variance is between -1 second to +10 seconds per day for calibers 9S67, 9S65, 9S56, 9S55, 9S54 and 9S51, and -1 second to +8 seconds per day for caliber 9S85.