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A NEW SPRING DRIVE<br />
Last year when we were invited to Seiko’s Shizukuishi Watch<br />
Studio for a visit, we heard whispers of a new movement<br />
that would be released in 2020 to commemorate their 60th<br />
anniversary. Now, both movements have been unveiled<br />
and it’s not just one but two movements that have been<br />
presented. The 9RA5 caliber is a Spring Drive development<br />
while the 9SA5 is a mechanical watch movement.<br />
Seiko’s Spring Drive has long been well-respected<br />
in the industry since it first appeared in 1999. To quickly<br />
recap, the movement essentially runs like a regular gear<br />
train, except that the balance wheel is instead replaced with<br />
a “glide wheel” that acts like the fixed fourth wheel of the<br />
movement and drives the seconds hand. The regulation<br />
of the gear train is by an electromagnet, which brakes the<br />
motion of the wheel to keep it constant. The system delivers<br />
256 brakes per second, controlled by a samadium-cobalt<br />
electromagnet that has 25,000 coils.<br />
The winding system is bi-directional and controlled by<br />
a lever that was developed in-house by Seiko in 1959. In<br />
the new 9RA5 movement, the Magic Lever, as it is known,<br />
is now off-set from its old placement at the centre of the<br />
movement, which means the caliber slims down. Two<br />
barrels power the movement, in differing sizes, and run<br />
in overlapping series so as to deliver a very even torque<br />
throughout the movement’s power reserve, while lasting<br />
for 120 hours. In addition, a single piece bridge has been<br />
developed and machined, that’s meant to secure the new<br />
layout of the gear train. This single center bridge provides<br />
significant shock resistance for the movement, up to ISO<br />
6425 requirements.<br />
The new caliber is also more precise thanks to an<br />
improved integrated circuit that has a sensor to monitor the<br />
temperature of the movement. Since quartz is temperature<br />
sensitive, the circuit board compensates for any fluctuations<br />
in the oscillation rate.<br />
The first watch to bear the new 9RA5 caliber is the<br />
Grand Seiko 60th Anniversary Limited Edition Professional<br />
Diver’s Watch 600M reference SLGA001, to be made<br />
available to customers in a limited edition of 700 pieces<br />
from August 2020 onwards. The movement offers a<br />
precision of 10 seconds per month, or 0.5 seconds a day.<br />
The case and bracelet are in high intensity titanium, a Grand<br />
Seiko material that’s also seen in its 60th anniversary special<br />
editions. The material has double the hardness of steel while<br />
maintaining the light weight of titanium, along with a 600<br />
meter water resistance and the movement is magnetically<br />
shielded, according to ISO 6425 requirements. The crown,<br />
like all Seiko diving watches, is screw-down and positioned<br />
at four o’clock, rather than three, a Seiko characteristic. The<br />
bracelet also has an easy extension function for a convenient<br />
fit over a diving suit and a secure lock.<br />
Above<br />
The Grand Seiko<br />
reference 3180<br />
from 1960.<br />
Left<br />
The Grand Seiko<br />
60th Anniversary<br />
Limited Edition<br />
Professional<br />
Diver’s Watch<br />
600M SLGA001.<br />
Featured below is<br />
the 9RA5 Spring<br />
Drive caliber, with<br />
twin barrels, an<br />
off-set Magic Lever<br />
and a single center<br />
bridge for enhanced<br />
shock resistance.<br />
102 BACKTOTHEFUTURE
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