Grand Seiko Spring Drive UFA Ushio 300 Diver: The Most Accurate ISO 6425 Dive Watch
Grand Seiko Redefines Precision with ISO 6425-Certified Spring Drive UFA Diver
Grand Seiko has unveiled its most compact and accurate dive watch to date with the Spring Drive UFA Ushio 300 Diver, references SLGB023 and SLGB025. These new models represent a significant evolution for the Japanese luxury brand's dive watch collection, addressing long-standing criticisms about size while delivering unprecedented precision for a dive instrument.
Breaking Down the Specifications
The Ushio 300 Diver marks a turning point for Grand Seiko's dive watch program. At 40.8mm in diameter and 12.9mm thick, these titanium-cased timepieces are roughly the same size as a modern Rolex Submariner Date—a deliberate move to compete in the highly competitive 300m luxury diver market.
| Specification | Grand Seiko SLGB023/SLGB025 |
|---|---|
| Case Diameter | 40.8mm |
| Thickness | 12.9mm |
| Case Material | High-Intensity Titanium |
| Water Resistance | 300m (ISO 6425 compliant) |
| Movement | Spring Drive Calibre 9RB1 |
| Accuracy | ±20 seconds per year |
| Power Reserve | 72 hours |
| Bezel | 120-click unidirectional, ceramic insert |
| Dial Colors | Gradient blue (SLGB023), Gradient green (SLGB025) |
| Bracelet | High-Intensity Titanium with micro-adjust clasp |
| Price | EUR 12,500 |
The Spring Drive UFA Advantage
At the heart of these dive watches lies the Calibre 9RB1, a Spring Drive movement featuring Ultra Fine Accuracy (UFA) technology. This hybrid movement combines the self-winding convenience of a mechanical movement with the precision of a quartz regulating organ, achieving an accuracy of ±20 seconds per year—approximately ±3 seconds per month.
The no-date display ensures the presence of luminous markers all around the dial, satisfying ISO 6425 requirements for low-light legibility while providing a balanced aesthetic.
Design Evolution for Everyday Wearability
Grand Seiko's Evolution 9 design language is clearly present in the Ushio 300 Diver. The thinner profile, curved caseband, and more ergonomic proportions make these watches suitable for both underwater use and daily wear. The rectangular applied markers replace the smaller round markers of previous GS divers, offering more luminous surface area and visual consistency.
Availability and Pricing
The Grand Seiko Spring Drive UFA Ushio 300 Diver SLGB023 and SLGB025 are permanent collection pieces available from June 2026. The blue SLGB023 will be available from all retailers, Master Shops, and official boutiques, while the green SLGB025 is reserved for dedicated salons and official brand boutiques.
At EUR 12,500, these watches compete directly with the Rolex Submariner Date (EUR 11,000-11,550) while offering superior accuracy, titanium construction, and Grand Seiko's distinctive finishing.
Frequently Asked Questions
How does the Spring Drive UFA achieve such high accuracy?
The Spring Drive technology combines a mechanical mainspring with a quartz-controlled electronic regulator. The UFA designation indicates enhanced manufacturing processes for the quartz oscillator and newly designed IC components, achieving accuracy that surpasses both purely mechanical and standard Spring Drive movements.
Is the green SLGB025 harder to purchase?
Yes, the green SLGB025 is a limited distribution model available only from Master Shops and official Grand Seiko boutiques. The blue SLGB023 has broader availability through all authorized retailers.
Sources: Monochrome Watches, Grand Seiko Official
Discover more about our Grand Seiko collection and explore the full range of Spring Drive timepieces.