Ushio 300 Diver

In 2025, Grand Seiko unveiled the Spring Drive Caliber 9RB2, a groundbreaking movement that received the then-new U.F.A. designation, standing for “Ultra Fine Accuracy.” Boasting an annual accuracy rate of ±20 seconds, Caliber 9RB2 earned the distinction of being the most accurate wristwatch movement powered by a mainspring.* This model is powered by Caliber 9RB1, featuring an improved construction that makes it ideal for sporting conditions while sharing the same attributes as the Caliber 9RB2. The term ushio, which means “tide” in Japanese, evokes the waters that surround the Japanese archipelago. This creation’s blue dial reflects the vast expanse of the sea through a gradient that captures light streaming into the deep ocean. *As of April 2026, based on Grand Seiko’s research.