Monochrome Watches
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The Grand Seiko Minamo SLGA007 & Tree-Rings SLGA008, With 5-Day Spring Drive Calibre 9RA2 (Live Pics)

A new pair of watches with the recent design cues, and a strong movement.

| By Brice Goulard | 7 min read |
Grand Seiko Minamo SLGA007 calibre 9RA2 Spring Drive 5-day

Grand Seiko has been extremely productive this year, which makes sense since the company is celebrating the 140th anniversary of its foundation, when Kintaro Hattori created its watchmaking atelier in 1881. We’ve already seen impressive watches, such as the SLGH005 White Birch or the SLGH007 Tree-Rings, both using the brand’s recent design language with mechanical movements. Based on the same vision, today the Japanese high-end watchmaker applies it to two new models that also feature an unprecedented movement, the 5-Day Spring Drive Calibre 9RA2, with the new Grand Seiko Minamo SLGA007 & Tree-Rings SLGA008.

Slim and powerful, the new Calibre 9RA2

As such, this movement isn’t entirely new, as it is based on the same architecture as the 9RA5 that was first introduced on the Professional Diver 600m SLGA001 in early 2020. And if the new 9RA2 is a development over this existing (yet recent) base calibre, it is the first time we see it moving into the Heritage collection, which necessitates to come back to what it means for the brand.

One of the main differences between the 2020 Calibre 9RA5 and this new Calibre 9RA2 is the location of the power reserve indicator, here positioned on the back side of the movement for a cleaner display dial side.

First and foremost, this movement is using the brand’s exclusive Spring Drive technology, a hybrid type of movement that capitalizes on the benefits of quartz regulation and the beauty and “perpetuity” of an automatic watch. 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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The 5-Day Spring Drive Calibre 9RA2 as seen through the caseback of the Tree-Rings SLGA008

The new 9RAX generation is a strong upgrade over existing movements, such as the 9R6x architecture. It improves all elements – size, performance, decoration and functionality – and set a new standard for any spring-powered watch. The result: about 60% more power reserve, almost 1mm less in height, a much faster date mechanism and even better accuracy. 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. 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.

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. The new Spring Drive 9RAX incorporates two barrels that 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.

While the previous generation of Spring Drive movements was given for an already impressive ±15 seconds per month accuracy rate, Caliber 9RAX 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.

The Grand Seiko calibre 9RA2 Spring Drive, as seen in the Minamo SLGA007

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 Minamo SLGA007

First model in this new pair of Heritage Spring Drive models is named “Minamo” and goes under the reference SLGA007. A quick look at it leaves no doubt on its lineage, being almost identical in shape with the SLGH005 White Birch. Indeed, it features the same angular and redesigned case with a flat, straight brushed bezel, innard angle inside the lugs, polished accents on the sides and overall a more modern, less bulky design. Dimensions are still relatively reasonable, with a 40mm diameter and 11.8mm in height. This version is worn on a stainless steel bracelet with a folding clasp decorated with the Grand Seiko initials in 18k gold.

As often with Grand Seiko, most of the beauty of the watch is to be seen on the dial, as once again the watchmaker has created a texture inspired by nature. For this new model, the dial “evokes the gentle sway of the water surface of Lake Suwa, with ripples
and shallow waves that create a pleasing sparkle at whichever angle the dial catches the light.” In other words, the dial is dark blue coloured with a fine, relatively discreet texture that looks like the surface of water. It is combined with the slightly refreshed applied indexes and hands, still finished with an impressive level of detail. Finally, the GS logo and the seconds are gold-coloured, “echoing the morning sunrise shimmering on the lake’s surface” and giving a warmer, more appealing touch to this watch.

Thanks to the new Calibre 9RA2, the SLGA007 has a clean, time-and-date display with the power reserve nicely located on the back of the watch. Through the sapphire crystal, the beautifully finished movement is visible with its elegant oscillating weight and blued screws and a blued power reserve hand. As said, the movement is powerful with 120 hours of energy and extremely precise, with a claimed accuracy of ±0.5 seconds per day.

The Grand Seiko Heritage Minamo SLGA007 will be limited to 2,021 pieces and available as of December 2021 in Grand Seiko Boutiques and selected retail stores worldwide. Price is set at EUR 9,100.

Quick Facts: 40mm x 11.8mm – stainless steel case, sapphire crystals, 100m water-resistant, screw-down crown – textured blue dial – Spring Drive 5 Days Calibre 9RA2, 34mm x 5mm, 38 jewels, automatic winding – stainless steel bracelet with folding clasp – 2,021 pieces – EUR 9,100

The Grand Seiko Tree-Rings SLGA008

The second watch to be introduced today by Grand Seiko will certainly feel familiar to you, as it is the Spring Drive pendant to the high-end, platinum-case Tree-Ring Limited Edition SLGH007. As such, it relies on the same basic design cues, meaning the same case as this platinum watch, but also the same case design as the Minamo above or the White Birch. There is one major difference though, even if the dimensions are identical – 40mm x 11.8mm – the case is here executed in 18K rose gold. It is worn on a brown crocodile strap with a three-fold clasp with push-button release in 18k rose gold.

In the same vein as the SLGH007, this new Grand Seiko Tree-Rings SLGA008 features a dial with a texture inspired by nature, with its minuscule variations in depth to recreate the dark and light tones of wood grain. It is here presented in a dark brown tone that matches nicely with the warm colour of the gold case. The bold, faceted applied markers and hands are also done in this same precious metal.

Powered by the new calibre 9RA2, this Tree-Rings SLGA008 will be available as a limited edition of 140 pieces at the Grand Seiko Boutiques and selected Grand Seiko retailers worldwide in November 2021. Price is set at EUR 50,000.

Quick Facts: 40mm x 11.8mm – 18K rose gold case, sapphire crystals, 100m water-resistant, screw-down crown – textured brown dial – Spring Drive 5 Days Calibre 9RA2, 34mm x 5mm, 38 jewels, automatic winding – crocodile strap with folding clasp – 140 pieces – EUR 50,000

For more details, please visit Grand Seiko.

2 responses

  1. Looking forward to the gold one being available on Chrono 24 at a more reasonable price point. 50k is Patek money, and nice though it is, it isn’t.


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