At the heart of Caliber 9SA5 is the Grand Seiko Free-sprung Balance. It may be less than one centimeter in diameter but it is the component that is most critical to the achievement of the high precision rate of +5 - -3 seconds a day. Created especially for this movement, it incorporates an overcoil whose shape was determined after more than 80,000 simulations and that optimizes the watch’s performance in every possible position. This is Grand Seiko’s first overcoil and has a unique design with four screws recessed in the rim of the wheel that can be turned to adjust the moment of inertia. As there is no regulator, the durability of the hairspring is increased, as is the precision over time.
This balance was created in 2020 for Caliber 9SA5 but is now also incorporated in Caliber 9SC5, the TENTAGRAPH automatic chronograph. In conjunction with the Dual Impulse Escapement and the Twin Barrel system, the Grand Seiko Free-sprung Balance makes a vital contribution to the creation of these two high-beat calibers with their high precision, excellent durability and extended power reserves.