Watches & Wonders 2026: Grand Seiko Spring Drive U.F.A. Ushio 300 Diver – The most precise and compact Spring Drive diver in the brand’s portfolio

With the new Spring Drive U.F.A. Ushio 300 Diver models SLGB023 and SLGB025, Grand Seiko expands its Evolution 9 Collection at Watches and Wonders 2026 with two diving watches powered for the first time by the new Spring Drive calibre 9RB1 and featuring a case diameter of 40.8 mm. These Spring Drive U.F.A. Ushio 300 Diver releases represent the smallest and most precise diving watches ever equipped with a Spring Drive movement by Grand Seiko. Here is a closer look at the new Spring Drive U.F.A. Ushio 300 Diver models.

The new Spring Drive calibre 9RB1

With its Spring Drive movement, Grand Seiko pursues a form of rate regulation that fundamentally differs from the mechanical solutions employed by its Swiss counterparts. Instead of a conventional escapement mechanism, it uses a so-called “glide wheel”, which is regulated and braked by a quartz oscillator and an electronic control circuit. At the same time, the entire Spring Drive system operates without a battery, as the quartz module is powered purely mechanically via the mainspring.

Patented in the late 1970s and first presented in 1988, the Spring Drive movement ultimately culminated in the Spring Drive calibre 9R65, introduced in 2004. This calibre marked a significant departure from the brand’s earlier movements: it combined automatic winding and a power reserve of 72 hours with a movement technology capable of achieving a monthly rate accuracy of ±15 seconds.

In 2025, at Watches and Wonders, Grand Seiko unveiled the next major development step of the Spring Drive movement: the automatic calibre 9RB2, also offering a 72-hour power reserve. Bearing the designation “Spring Drive UFA” – with “UFA” standing for “Ultra Fine Accuracy” – the new calibre achieves an accuracy of ±20 seconds per year. That is not per day, week or month, but per year. This level of precision, equivalent to approximately ±3 seconds per month and thus 12 seconds more accurate than its predecessor, led Grand Seiko to claim the launch of the most precise wristwatch powered by a mainspring.

The movement achieves this level of precision through new and improved manufacturing and finishing methods applied to both the quartz oscillator and the integrated circuit. In addition, the new movement introduces, for the first time in a Spring Drive calibre, a regulation mechanism that can be used during servicing to correct deviations in rate accuracy that may occur over prolonged use.

Now, one year later, Grand Seiko brings its Spring Drive UFA technology to a diving watch for the first time, with the two new Evolution 9 Spring Drive U.F.A. Ushio 300 Diver models SLGB023 and SLGB025, powered by the new Spring Drive calibre 9RB1. The movement is hand-assembled at the Shinshu Watch Studio in the city of Shiojiri, located in the centre of Nagano Prefecture, and measures 30 mm in diameter with a height of 4.7 mm—dimensions that also allow for a notably compact case design.

Water resistance, construction and legibility of the new models

Diving watches have long since evolved beyond being purely functional tools for professional divers—they have also become one of the most popular categories among collectors. However, not every watch that looks like a diver is necessarily suitable for actual diving: for a watch to be officially designated a “diver’s watch”, it must meet specific requirements, primarily defined by the international ISO 6425 standard. These criteria relate in particular to water resistance, legibility and robustness. Grand Seiko itself states that its new diving models are designed for professional use—so it is worth taking a closer look at the construction of the Spring Drive U.F.A. Ushio 300 Diver models and the standards they fulfil.

At the top of the list is water resistance, which, according to ISO 6425, must be rated to at least 100 metres, with actual pressure testing carried out at 25% above the stated depth rating. In the case of the new Spring Drive U.F.A. Ushio 300 Diver models, this would correspond to a test pressure of approximately 37.5 bar—25% above the declared water resistance of 300 metres (30 bar). The Spring Drive U.F.A. Ushio 300 Diver watches are housed in a case measuring just 40.8 mm in diameter and 12.9 mm in height, made possible by the compact construction of the movement, and therefore noticeably smaller than previous Grand Seiko diver’s watch cases.

In addition to water resistance, legibility is a central requirement for any diver’s watch. ISO 6425 specifies, among other things, continuous minute markings, clearly legible markers at five-minute intervals, and a luminous reference marker on the bezel—typically in the form of a triangle—to indicate dive time. To meet these requirements, the new Spring Drive U.F.A. Ushio 300 Diver models are equipped with a unidirectional rotating bezel featuring 120 clicks for precise adjustment and incorporating all the prescribed characteristics. A ceramic insert, executed in either blue or green depending on the version, ensures resistance to scratches and corrosion.

Legibility under low-light conditions is also defined by ISO 6425: after prior exposure to light, the watch must remain clearly readable in darkness from a distance of 25 cm. Accordingly, the bezel markings, hands, and rectangular indices of the new Spring Drive U.F.A. Ushio 300 Diver models are generously coated with the green luminous material Lumibrite. The dials continue the “Ushio” design motif, which has been part of Grand Seiko’s diver’s watches since 2022, and are presented in two colour variations: the blue dial reflects the depth of the open sea, while the green version is inspired by shallower coastal waters. Both models are unified by a gradient that transitions from a darker tone at the periphery to a lighter shade towards the centre of the dial. A functional update concerns the power reserve indicator, which has been moved to the dial side.

Another key requirement for a diver’s watch is corrosion resistance. According to ISO 6425, this is assessed by means of a salt spray test; 48 hours after exposure, neither the watch itself nor the bracelet should show any significant visual or tactile changes. To meet this requirement, both the case and bracelet of the new Spring Drive U.F.A. Ushio 300 Diver models are made from “High-Intensity Titanium”, a material that, according to the brand, is around 30% lighter than stainless steel. The bracelet features a newly developed folding clasp with a safety mechanism and an integrated fine-adjustment system. This allows for a three-step adjustment of up to 6 mm, as well as an additional extension of 18 mm—for example, for use over a diving suit—resulting in a total adjustment range of 24 mm.

Price & availability of the new Grand Seiko Spring Drive U.F.A. Ushio 300 Diver models

The new Grand Seiko Spring Drive U.F.A. Ushio 300 Diver models will be available worldwide from June 2026 through Grand Seiko boutiques and selected retail partners, each priced at €12,500.

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