Grand Seiko T0

The Grand Seiko caliber T0 (T-Zero) is a prototype tourbillon movement announced in 2020, based on the 9S65 caliber. It operates at 28,800 vph and achieves chronometer-grade accuracy of +/- 0.5 seconds per day. The T0 is notable for integrating a constant-force mechanism and tourbillon on the same axis—a first in watchmaking—allowing the escape to receive consistent torque throughout the power reserve. Developed at Grand Seiko Studio Shizukuishi in Morioka, Japan, the movement was created as an unrestricted concept study and served as a development template for the later 9SA5 hi-beat caliber. It remains a non-production prototype displayed at the studio.