Grand Seiko Professional Diver's 600M Watch SLGA001

As one of the novelties introduced for the brands 60th anniversary, Grand Seiko gave the SLGA001 Limited Edition 600M Professional Divers the honor of presenting its all-new Spring Drive caliber. The 9RA5 caliber is slimmer, more precise, and has a greater power reserve than its predecessor.Grand Seiko Professional Divers 600M?Spring DriveIn my first article on the Spring Drive principle I think it was early 2006 I said Spring Drive was a solution to a problem that didnt exist. That proved to be only partly true. The problem didnt exist indeed, but Spring Drive wasnt meant to be a solution. It became clear that it was an innovation. It was (and still is) an entirely new way of regulating a mechanical movement. Since its debut, it has stood alone. It is something new something that sits apart from the rest of the industry.As such, Ive grown to love the Spring Drive movement family. Im a big fan and have a lot of respect for the Spring Drive system. If you want to learn more about the construction of Spring Drive and how it exactly works, I can recommend Grand Seikos dedicated Spring Drive website and one of our Sunday Morning Showdown articles in which Rob uses the way the Spring Drive works as the cornerstone of his argument for the Skyflake over s Sky-Dweller.Improvements to the standard Spring Drive caliberFrom 2005 onwards, Grand Seiko used caliber 9R65 for most of their regular Spring Drive models. This now over 16-years old was mainly aimed at reliability and sturdiness. As a result, it wasnt one of the sleekest movements around.thickness 5.0mmThanks to the new gear train, moved towards the center of the movement with a central bridge that holds the wheels together, the new caliber didnt lose its reliability and sturdiness. However, thanks to this new layout, the thickness of the new caliber 9RA5 has been decreased substantially.power reserve 5 daysEven with the new thickness of 5.0 mm which is pretty much average for three-hand automatic calibers Grand Seiko managed to improve the power reserve. By the use of two differently sized main-spring barrels, it increased from 3 to 5 days or 72 to 120 hours. A dial-side power reserve indicator remained available for the new 9RA5 caliber. It shows at the left side in the dial but rises slightly above the center while formerly it was positioned below. Were getting to the watch in a minute, but for me, a power reserve indicator could have been omitted in a professional divers watch.accuracy +/- 10 seconds/monthLast but not least. Not only the power reserve increases but the accuracy as well. Now equipped with a temperature-compensated quartz crystal, the accuracy of the new 9RA5 caliber exceeds plus or minus 10 seconds a month.SLGA001, a Limited Edition Professional Divers WatchAs you probably know, the new SLGA001 Professional 600M Divers Watch isnt Grand Seikos first divers watch with a Spring Drive movement. Weve seen the SBGA229 (which we reviewed here) and even a titanium counterpart of that watch, the SBGA231. However, the depth rating of these two models was 200 meters. Thats adequate as a recreational divers watch and sufficient to comply with the ISO 6425 diving standard.The now-introduced SLGA001 is a Professional Diver. At Grand Seiko, this not only means a higher depth rating. It also means that this watch is suitable for saturation diving. For saturation purposes, a dive watch needs a different construction. Its necessary to seal the watch in a way preventing not only water to enter the casing under high pressure, but helium gas as well. To learn more about the weird, dangerous, isolated life of a saturation diver, Id suggest you visit this page.Smaller movement, larger caseContrary to the new Spring Drive caliber, the SLGA001 watch, as such, didnt decrease in size. Compared to the Spring Drive models mentioned earlier, it even gained 2.7 mm in diameter and 2 mm in height. The reason for this is the increased depth rating and the ability to be used for saturation diving.I dont think that a diameter of almost 47 mm should be considered too big for a professional divers watch. Grand Seikos other 600-meter-rated Professional Diver, the SBGH255 with caliber 9S85 hi-beat movement, sports the same diameter. But it leaves me a bit puzzled why exactly Grand Seiko chose the SLGA001 to present a new slimmer Spring Drive caliber.home-grown titaniumTo keep the weight of such a large watch within the bounds of reason, Grand Seiko made the case in High-Intensity Titanium. This home-grown material is 40% lighter than steel and is more resistant to scratches.On top of the titanium casing, we find a high-definition sapphire crystal and a uni-directional high-intensity titanium rotating bezel. The case and crystal are designed for easy and safe disassembly for maintenance that a professional diver demands.