Grand Seiko caliber 9R15
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The Caliber 9R15 is a movement that is specially adjusted to a higher precision than the most standard 9R spring drive movement, the Caliber 9R65.
While the caliber 9R65 has an average monthly difference of ± 15 seconds (equivalent to a daily difference of ± 1 second), the caliber 9R15 has a difference of ± 10 seconds (equivalent to a daily difference of ± 0.5 seconds).
The difference between the two movements lies in the quartz crystal that sends an accurate electrical signal.
All 9R spring drives use crystal units with stable accuracy, but only the crystals that exhibit particularly excellent performance are selected and installed in the “caliber 9R15”.
As a proof of the special adjustment accuracy, the rotor weight is made of 18K yellow gold and can be seen from the back cover of the see-through specification.