Grand Seiko Spring Drive U.F.A. 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. The green dial draws from the tranquil beauty of shallow coastal waters near the shore.