Evolution 9 Spring Drive U.F.A. Ushio 300 Diver SLGB023
The “Ushio 300,” a Spring Drive diver’s watch with phenomenal accuracy and a stunning blue dial
Features
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.
Specifications
| Exterior: | High-Intensity Titanium |
|---|---|
| Case back: | Screw case back |
| Glass Material: | Sapphire crystal |
| Glass Coating: | Anti-reflective coating on inner surface |
| LumiBrite: | LumiBrite on hands, index(es) and bezel |
| Case size: | Diameter 40.8mm Lug-to-lug 48.5mm Thickness 12.9mm |
| Band width: | 21mm |
| Clasp type: | Locking extension clasp with micro-adjustment |
| Caliber no.: | 9RB1 Instructions |
|---|---|
| Movement Type: | Spring Drive |
| Power reserve: | Approx. 72 hours(3 days) |
| Accuracy: | ±20 seconds per year (±3 seconds per month) |
| Water resistance: | 300m / 1000ft diver's |
|---|---|
| Magnetic resistance: | 4,800 A/m |
| Other details / Features: |
|
A sports watch true to the ideals of Grand Seiko
Like every Grand Seiko watch, the Ushio 300 strikes a perfect balance between function and beauty. Its legibility, durability, and wearing comfort have been thoroughly considered and painstakingly engineered to ensure uncompromising performance in any environment. Commensurate attention has been given to every aspect of the watch’s physical appearance.
The prominent indexes of the Evolution 9 Style are meticulously crafted with multiple facets. Both the hour and minute hands strike a sharply defined and powerful form, ensuring outstanding legibility at a glance.
“Ushio,” a dial that evokes the waters that surround the Japanese archipelago
The watch showcases a blue variation of the “Ushio” dial, a design theme that has been part of the Grand Seiko diver’s watch since 2022. The term ushio, which means “tide” in Japanese, evokes the waters that surround the Japanese archipelago, a timeless source of inspiration in Japan’s culture and art. Combined with a gradient design, the vivid dial color emphasizes the “Ushio” pattern while ensuring the excellent legibility for which Grand Seiko divers are renowned. The blue dial reflects the vast expanse of the sea through a gradient that captures light streaming into the deep ocean.
Enduring strength meets comfort and versatility
Thanks to the movement’s compact design, this model features a case diameter of just 40.8 mm, the smallest of any Grand Seiko diver’s watch, ensuring a comfortable fit for a wide range of wrist sizes. Both the case and bracelet are crafted from High-Intensity Titanium, a material approximately 30% lighter than stainless steel and distinguished by its bright, lustrous appearance.
Locking extension clasp with micro-adjustment
The bracelet includes a locking extension clasp with micro-adjustment. In addition to a three-step micro-adjustment that allows for up to 6 mm of fine-tuning, the extension feature, designed to be used with a diving suit, enables an additional 18 mm, for providing a total of 24 mm of adjustment.
Caliber 9RB1
The 9RB1 movement is hand-assembled by the highly skilled craftspeople of the Shinshu Watch Studio, located in a Seiko Epson facility in the city of Shiojiri in Nagano Prefecture.
While the Caliber 9RB1 shares the same attributes as the Caliber 9RB2, its power reserve indicator is located on the dial side.
