This month Grand Seiko introduced two Soko Special Editions wristwatches powered by Spring Drive movements and available only in the United States.

In Japan, sōkō means the end of Autumn, when the first frost embraces the forest. Accordingly, Grand Seiko states, “The green accent colors featured on the seconds hand and power reserve indicator epitomize the life of the Arashiyama bamboo forest in Kyoto in its peak season at the end of Autumn.”

The vertical texture on the dials reflects the stalks of the bamboo in the forest. The Soko US Special Editions come in two dial variants: the “light” – silver dial of (Ref. SBGA427) and “shadow” gray dial of (Ref. SBGA429).

Spring Drive is a unique type of watch movement developed by Seiko/Grand Seiko that combines the high torque of a mechanical watch with the high precision integrated circuit (IC) control system of an electronic quartz watch. Driving time and date functions is Grand Seiko Spring Drive caliber 9R65 which has 30 jewels and a 72-hour power reserve.

There’s a mainspring (like in a mechanical watch) instead of a battery, and a rotor winds the mainspring via movements of your wrist, also like a mechanical watch. This is where the Spring Drive differs from a mechanical watch that uses an escapement system to regulate the release of energy from the mainspring to the hands. Spring Drive utilizes an exclusive speed control mechanism, incorporating an IC, an electronic brake, and a quartz crystal. The result is incredible precision (similar to quartz), with no need for a battery (like a mechanical).

Not only is the timekeeping more accurate, at a rated -/+ 1 second per day (or -/+ 15 seconds per month) — compared to -4/+6 for a standard COSC certified chronometer — the release of energy is able to be so well controlled that the hands sweep incredibly smoothly, a signature of the Spring Drive.

The watch comes in a contemporary Grand Seiko case made of stainless steel that measures. 39 mm x 12.5 mm. The dial is protected by a curved sapphire. And a screw-in see-through caseback offers a view of the Spring Drive movement on the back.

Each of the Soko editions with both a stainless steel bracelet and a brown alligator strap with contrast stitching in the same green shade as the second hand and a stainless steel bracelet. The strap and bracelet each have a steel folding push-button deployant clasp.