Seikoin-house caliber 9S85A found in a Grand Seiko automatic watch. The Spron 610 hairspring is anti-magnetic.
The heart of the mechanical watch is its movement. A “10-beat” movement means that the balance, the most important component for determining the accuracy of a watch, vibrates at 10 beats, or oscillations, per second. Mechanical watches, even luxury watches, operate at 5 to 8 beats per second. A higher number of vibrations makes a watch more resistant to shock, controlling fluctuations in dynamic accuracy—the watch’s accuracy while being worn—to keep the time correctly and with stability. Seiko has succeeded in producing the Grand Seiko with a 10-beat movement, caliber 9S85. The watch is highly resistant to disturbance with minimized accuracy fluctuation when worn.