Grand Seiko Launches Most Compact Diver With Spring Drive Ushio 300

Grand Seiko has unveiled the Spring Drive U.F.A. Ushio 300, a new dive watch that distinguishes itself as the brand's most compact diver to date. This timepiece is engineered to embody Grand Seiko's philosophy of harmonizing exceptional utility with understated beauty, merging robust diving performance with refined horological engineering. The core of this integration is the Spring Drive Caliber 9RB1 movement, a 33-jewel self-winding caliber that has earned the "Ultra Fine Accuracy" (U.F.A.) designation. This movement boasts an impressive annual accuracy rating of ±20 seconds, which translates to approximately ±3 seconds per month, positioning it among the most accurate wristwatch movements powered by a mainspring.

The precision of the Caliber 9RB1 is achieved through meticulous micro-engineering at Grand Seiko's Shinshu Watch Studio in Shiojiri, Nagano Prefecture. Skilled watchmakers hand-assemble the movement, which incorporates a vacuum-sealed crystal oscillator paired with a low-power integrated circuit (IC). To ensure optimal stability, each oscillator undergoes a rigorous three-month aging process for frequency stabilization. Following this, its frequency is measured across a range of temperatures, and this data is then programmed into the IC for precise thermo-compensation. This sealed capsule design is crucial for minimizing the influence of external environmental factors such as temperature fluctuations, humidity, static electricity, and light, all of which can affect timekeeping accuracy.

Designed with long-term serviceability as a priority, the Caliber 9RB1 includes an integrated regulation switch. This feature allows for after-sales service adjustments to correct any potential divergences in accuracy that may arise over extended periods of use. The movement also provides a substantial 72-hour power reserve, indicated by a dial-side power-reserve indicator. The compact nature of the caliber, measuring 30.0mm in diameter and 4.7mm in thickness, is instrumental in Grand Seiko's ability to create a highly capable tool watch that can seamlessly transition from demanding underwater environments to everyday wear. This slim movement architecture directly supports the brand's objective of crafting a diver's watch with exceptional functionality and refined proportions, making it Grand Seiko's most compact diver to date.