Grand Seiko · Evolution 9 Collection
Grand Seiko SLGA021: specifications and what to check
One hundred and twenty hours, and a power reserve indicator you can only read by taking the watch off. Five days of reserve changes how the watch is owned and how it is inspected.
Reference SLGA021 · specifications read from the manufacturer on 2026-09-22 · listed as current
Specifications
As published by Grand Seiko. A field the manufacturer does not state is left out rather than filled in.
- Case
- Stainless steel, 40.0 mm, described as embodying the Evolution 9 Style
- Diameter
- 40 mm
- Thickness
- 11.8 mm
- Lug width
- 22 mm
- Lug to lug
- 47.9 mm
- Water resistance
- 10 bar
- Crystal
- Dual-curved sapphire crystal, anti-reflective coating on inner surface
- Dial
- Blue with a textured pattern, described as expressing the surface of Lake Suwa before dawn
- Case back
- Movement visible from the back, with a decoration described as Shinshu Frost
- Bracelet
- 22 mm band width
- Clasp
- Folding clasp with push button release
Movement
- Calibre
- 9RA2
- Type
- Spring Drive, self-winding with manual-winding
- Power reserve
- Approximately 120 hours (5 days)
- Notes
- Stated accuracy ±10 seconds per month (±0.5 second per day). Described as compensating for variations in the oscillator's performance by measuring the temperature 540 times per hour. The power reserve indicator is on the back rather than the dial, which Grand Seiko says slims the profile. Total weight 176 g.
What to check before you buy
- Turn the watch over to read the power reserve. On this calibre the indicator is on the back, so an inspection that never leaves the dial side has skipped the most useful gauge the watch has.
- Allow five days, not one, to test the reserve properly. A movement specified at approximately 120 hours can hide a weak barrel through an overnight check that a shorter-reserve watch would fail immediately.
- Time it against ±10 seconds per month rather than a daily figure. That works out near half a second a day, so a watch losing several seconds daily is far outside its own specification.
- Check the textured blue dial across its whole surface at several angles. A patterned finish records handling and moisture in a way a plain dial conceals, and it cannot be retouched.
- Inspect the Shinshu Frost decoration on the movement through the back under a loupe. It is a finished surface on display, so marks, fingerprints and burred screw heads from a previous service are all visible.
Five days changes the inspection
Most of the references documented on this site hold somewhere between fifty-five and eighty hours. The 9RA2 is specified at approximately 120 hours — five days.
That sounds like a straightforward improvement and, for an owner, it is. For an inspector it cuts the other way.
The standard overnight reserve test works because a watch with two or three days of capacity has nowhere to hide: a tired barrel shows up in twelve hours. Here, a movement running at seventy percent of its designed capacity would still sail through a night, a weekend, and most of a working week without stopping.
So if you are going to test the reserve on this reference, test it properly: wind to full, note the indicator, and leave the watch untouched for five days. Anything shorter is not a test of a five-day movement, and knowing that is the difference between a real check and a ritual.
The gauge is on the other side
Grand Seiko moved the power reserve indicator to the case back on this calibre, and says the reason is to slim the watch's profile. The result is 11.8 mm thick on a 40 mm case, which is genuinely slim for an automatic with this much capacity.
The consequence for inspection is simple and easy to forget: turn the watch over. A dealer who works entirely from the dial side will never see the indicator at all, and will have skipped the one instrument the watch provides.
Get into the habit at the viewing, and tell the buyer about it at handover. More than one owner has assumed their five-day watch had no reserve display.
Half a second a day
The stated accuracy is ±10 seconds per month, which Grand Seiko also expresses as ±0.5 second per day.
Convert before you test, because the units mislead people in both directions. A watch that gains three seconds overnight sounds trivial next to a mechanical specification measured in seconds per day — but three seconds is six times this movement's daily allowance and roughly a third of its entire monthly budget.
Grand Seiko attributes the precision to a mechanism that measures temperature 540 times an hour and compensates for how the oscillator's performance varies with it. Whatever the method, the number is the standard you hold the watch to, and it is a much tighter one than anything mechanical on this site.
Dial and movement finish, both on display
The dial is blue and textured, described as expressing the surface of Lake Suwa before dawn. As with any patterned dial, look at it from several angles across the whole face rather than straight on once. Texture records what a flat finish hides — and there is no way to touch it up.
Through the back, the movement carries a decoration Grand Seiko calls Shinshu Frost. Treat it as an inspection surface rather than a flourish: under a loupe, a previous watchmaker's fingerprints, slips and burred screw slots are all sitting there in plain view.
For the listing: 40.0 mm diameter, 11.8 mm thick, 47.9 mm lug to lug, 22 mm lug width, 176 grams, 10 bar.
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Sources
Not affiliated with Grand Seiko. Specifications are read from the manufacturer's own published documentation on the date shown and may change; the manufacturer's current documentation governs.