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Grand Seiko Professional Diver 600m SLGA001, With New Spring Drive Calibre 9RA5

Slimmer, more precise and more powerful. A new Spring Drive movement makes it debut in a robust diver's watch.

| By Brice Goulard | 6 min read |
Grand Seiko Professional Diver 600m SLGA001 Spring Drive 9RA5

Dive watches and Seiko are a long and rich story – as we’ve seen earlier today with the 55th Anniversary Trilogy of dive watches. This expertise isn’t reserved to the praised Prospex collection and Grand Seiko, the high-end division of the Japanese brand, also benefits from this. Today, part of its 2020 collection, Grand Seiko introduces a new Spring Drive diver – ref. SLGA001 – based on a design already used with the Hi-Beat 36000 Professional 600m SBGH255. However, the main novelty isn’t here, but inside the robust titanium case, as the brand coincidentally release its brand new generation of Spring Drive movement, the 9RA5. Slimmer, more precise and more powerful.

Grand Seiko Professional Diver 600m SLGA001 Spring Drive 9RA5

A quick reminder about Spring Drive. Since 1999, Grand Seiko benefits for a third kind of movement, next to its classic mechanical or quartz calibres. Spring Drive is a hybrid, which aims at combining the best of both worlds. On one side, it features a self-winding capacity to have perpetual energy (and no battery). On the second hand, it capitalizes on the proven accuracy of a quartz regulator – which is known to be far more precise than a traditional balance/escapement couple. The result was a movement that looked almost identical to an automatic calibre, as still featuring multiple gears and wheels, just modified on the regulating part with an electronic regulator combined with a quartz crystal – the so-called “Tri-synchro regulator”.

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Until today, most of the Grand Seiko Spring Drive time-and-date watches were powered by the 9R6x architecture, with 72 hours of power reserve, a rather high profile and a nice but still quite industrial decoration. Today, the brand launches the new Calibre 9R35, which is slimmer, more powerful, more precise and even more pleasant to look at… And it makes it debuts in a professional diver’s watch.

The new 5-day Spring Drive Calibre 9RA5

Spring Drive, still a proprietary technology only used by Grand Seiko and Seiko, is today perfectly mastered by both brands. And now that the public has accepted the idea of a high-end watch powered by a hybrid movement, it was time for Grand Seiko to bring an array of improvements to its signature technology. And it is an ambitious development.

The idea of the Grand Seiko team was to improve all aspects of its Spring Drive movements – size, performance, decoration and functionality – set a new standard for any spring-powered watch. The result is a new generation of movement, with the calibre 9RA5. Compared to the current 9R6x generation, which is used for instance in the Snowflake SBGA211, we’re talking about 60% more power reserve, almost 1mm less in height, a much faster date mechanism and even better accuracy.

Grand Seiko Spring Drive Calibre 9RA5 5-day power reserve
Not only the 9RA5 is slimmer and more powerful, but the decoration is far more attractive than before.

Slimmer, but with more strength

The new Calibre 9RA5 is, first of all, a brand new architecture with redesigned plates and bridges. Also, new construction of multiple parts has made possible to reduce the thickness from 5.8mm to 5.0mm. One of the key elements of this reduction of height is the re-positioning of the Magic Lever.

Developed in-house in 1959, the Magic Lever boosts the efficiency of the automatic winding mechanism by using the energy created by the movement of the oscillating weight in both directions. In the new calibre, the new Offset Magic Lever is positioned away from the centre of the movement to reduce its thickness. Remarkably, this is achieved with no loss of winding efficiency. The stem and crown are also positioned towards the back of the case to lower the centre of gravity and achieve a comfortable fit on the wrist.

Grand Seiko Spring Drive Calibre 9RA5 5-day power reserve

While slimmer, the Calibre 9RA5 has enhanced rigidity and shock resistance thanks to the new layout of the gear train towards the centre of the movement and a central bridge that holds them together. This One-piece Center Bridge achieves a shock resistance that meets the ISO standard for diver’s watches.

Up to 5 days of power reserve

Previous generations of Spring Drive movements were already delivering a comfortable 3-day or 72-hour power reserve – enough to leave the watch away for a weekend and still having it working on Monday morning. But this wasn’t enough for Grand Seiko.

Grand Seiko Spring Drive Calibre 9RA5 5-day power reserve

The new Spring Drive 9RA5 incorporates two barrels which deliver a power reserve of up to 120 hours – the so-called “Dual-size Barrels.” They are different sizes so as to deliver the torque required for the 5-day power reserve while optimizing the use of the limited space within the movement.

New electronics for improved accuracy

While the previous generation of Spring Drive movements was given for an already impressive ±15 seconds per month accuracy rate, Caliber 9RA5 has an accuracy rate of ±10 seconds per month thanks to a new IC package and to the selection of highly stable quartz oscillators that have gone through a three-month ageing process.

Grand Seiko Spring Drive Calibre 9RA5 5-day power reserve
Grand Seiko’s brand new Spring Drive Calibre 9RA5 with a 5-day power reserve – also note the new decoration with matte surfaces for the bridges, blued screws, more opened rotor and bevelling all around

For the first time in a Spring Drive movement, the IC incorporates a sensor to measure the temperature within the movement and is programmed to compensate for any inaccuracies in the crystal oscillation rate which may be caused by temperature change. The oscillator and sensor are vacuum-sealed into a single package to eliminate even the slightest temperature difference between the two and this shield also reduces the possible influence of humidity, static electricity or light interference and thus maintains the watch’s accuracy at the highest possible level.

The Grand Seiko Professional Diver’s 600m SLGA001

To introduce this new Spring Drive 9RA5 Calibre, we would have expected a nice, elegant and high-end watch… But instead, Grand Seiko brings it in a robust, lightweight dive watch, the new Professional Diver’s 600m SLGA001.

Grand Seiko Professional Diver 600m SLGA001 Spring Drive 9RA5

This watch isn’t a novelty per se, but more the adaptation of a new technology in an already known habillage, introduced back in 2017 with the Automatic Hi-Beat SBGH255. It is one very serious diver’s, professionally-oriented, which has all the arguments to compete with the best of the industry – think Sea-Dweller or Planet Ocean.

Shaped in a typical Grand Seiko way, with sharp facets and a combination of brushed surfaces and polished accents, the SLGA001 is a massive but lightweight watch. The case measures 46.9mm in diameter and 16mm in height but is crafted in in high-intensity titanium, which is 40% lighter than steel and more impervious to scratches. The crown is located at 4 o’clock – a signature element of Seiko dive watches – and the date echoes this position on the dial. Note something specific on this watch; the case, crystal and bezel are all designed for easy and safe disassembly in order to clean the parts after a dive in salty waters.

Grand Seiko Professional Diver 600m SLGA001 Spring Drive 9RA5

The Grand Seiko Professional Diver’s 600m SLGA001 comes with all the usual features, such as a screw-down crown and screw caseback, a unidirectional bezel with ceramic insert, a hi-def sapphire crystal and is rated to 600m in saturation diving. The dial of this model is cleaner too, with a matte blue background, applied indexes and a power reserve positioned at 10 o’clock. All the indications are filled with Lumebrite.

The SLGA001 is presented in a special Grand Seiko 60th anniversary box, with a high-intensity titanium bracelet with folding clasp and diving extension, as well as an interchangeable blue silicone strap.

Grand Seiko Professional Diver 600m SLGA001 Spring Drive 9RA5

Price and availability

The Grand Seiko Professional Diver’s 600m SLGA001 will be a limited edition of 700 pieces, available worldwide in August 2020. It will be priced at EUR 11,500. More details at

4 responses

  1. The SBGA029 is 44/14. With discussion of of a thinner movement I also figured a slimmer case. Boy was I wrong!

  2. 16mm and its already thinner, its only a diver not a chronograph!

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