GS Grand Seiko

The power reserve remains the same, even when the chronograph is in use

When the stopwatch of a conventional mechanical chronograph is operated, the power reserve of the timepiece diminishes and, as the mainspring’s torque decreases, time measurement begins to lose precision. As in so many other ways, the Spring Drive chronograph breaks with convention and delivers superior performance. When the stopwatch is in operation, there is no decline in the power reserve and the watch’s precision remains the same, whatever the power in reserve. By using fewer wheels in the gear train and reducing by half the amount of electrical energy required by the brake to regulate the speed of the seconds hand, the development team was able to reduce energy transmission loss and maintain the power reserve.

The Grand Seiko Spring Drive chronograph is the most precise spring-driven chronograph in the world, delivering an accuracy rate of one second a day. This high level of precision in the movement is matched by the precision of the button operation. Thanks to the combination of a column wheel and a vertical clutch, the chronograph starts and stops without any loss of accuracy. Furthermore, the watch measures elapsed time exactly, thanks to the fact that the glide motion seconds hand stop at the very instant that the button is pressed and not to the nearest fraction of a second, as in every other spring-driven chronograph.

Calibre 9R86. The precision of the chronograph is further enhanced by the push button with a two stage READY/START operation. The pressure required to start and stop the chronograph is carefully calibrated to ensure exact timing.

Calibre 9R86 was completed in 2007. Thanks to the skill and diligence of Hara, Hiraya and many others, Spring Drive had evolved from a simple hand-winding three hand watch into an automatic chronograph with a 72-hour power reserve and a 24-hour GMT hand. An engineer’s dream in the 1970s eventually became a reality in 1997 and has continued to evolve ever since. Continuous improvement has always been, and still is, central to the character of Grand Seiko.