When Grand Seiko first showed the Spring Drive U.F.A. diver at Watches and Wonders in April, it was a teaser more than a product: a movement, a promise of accuracy, and not much else to hold onto. The full picture has now arrived. The watch ships as two references, the SLGB023 in blue and the SLGB025 in green, both priced at USD 12,400 and both reaching boutiques and selected retailers in June 2026.
The headline number is the accuracy. Inside is the new Caliber 9RB1, a Spring Drive movement carrying the U.F.A. designation, short for Ultra Fine Accuracy. It is rated to plus or minus 20 seconds a year, or roughly plus or minus three seconds a month. Grand Seiko introduced the first U.F.A. movement, the 9RB2, in 2025 and called it the most accurate mainspring-powered wristwatch movement it makes. The 9RB1 keeps that performance and reworks the construction for sporting use, moving the power reserve indicator to the dial side and freeing up the case.
How the accuracy is reached
Spring Drive runs on a mainspring but regulates itself electronically, against a quartz oscillator rather than a balance and escapement. For the U.F.A. calibres, Grand Seiko vacuum-seals the crystal oscillator alongside its integrated circuit, which limits the drift that temperature and humidity normally introduce. Each oscillator is then aged over several months and individually calibrated. The movement is hand-assembled at the Shinshu Watch Studio in Shiojiri, Nagano, holds 72 hours of power reserve and runs on 33 jewels.
A diver built down, not up
The more surprising part is the case. At 40.8mm across, 48.5mm lug to lug and 12.9mm thick, the Ushio 300 is the smallest diver Grand Seiko has made. That is unusual in a category where most brands add millimetres. The compact movement made the reduction possible, and the case and bracelet are both cut from High-Intensity Titanium, a material the brand says is roughly 30 percent lighter than stainless steel. The finished watch weighs 122 grams.
It remains a real dive watch. Water resistance is 300 metres, with a screw-down crown, a solid screw caseback, a unidirectional rotating bezel and LumiBrite on the hands, indexes and bezel. Magnetic resistance is rated to 4,800 A/m. The titanium bracelet uses a locking extension clasp with a three-step micro-adjustment good for 6mm of fine-tuning, plus an 18mm extension for use over a wetsuit, for 24mm of total range.
The dial does the talking
The name comes from the dial. Ushio means tide in Japanese, and the textured, gradient surface has been part of Grand Seiko's diver line since 2022. The SLGB023 reads as deep ocean, a blue gradient that suggests light falling through water. The SLGB025 takes a green that the brand associates with shallower, coastal water. In both, the faceted Evolution 9 indexes and sharply defined hands keep the watch legible, which is the point of a tool dial however decorative the texture.
There is a quiet logic to all of this. Grand Seiko's argument has rarely been complication; it has been precision, finish and restraint. A diver that is more accurate than almost any mechanical watch on the market, and physically smaller than the brand's own back catalogue, is an unusually direct expression of that. The teaser was the easy part. The watch holds up.
