Introducing Grand Seiko’s New Professional Diver, with a New Spring Drive Movement

Last year when we were invited to Seiko’s Shizukuishi Watch Studio for a visit, we heard whispers of a new movement that would be released in 2020 to commemorate their 60th anniversary event. Today, both movements have been unveiled and it’s not just one but two movements that have been presented. The 9RA5 caliber is a Spring Drive development while the 9SA5 is a mechanical watch movement, discussed here.

Seiko’s Spring Drive has long been well-respected in the industry since it first appeared in 1999 in Japan, with international release in 2005. So given that last year was Spring Drive’s 20th anniversary, we expected an update to the impressive movement.

To quickly recap, the movement essentially runs like a regular gear train, except that the balance wheel is instead replaced with a “glide wheel” that acts like the fixed fourth wheel of the movement and drives the seconds hand. The regulation of the gear train is by an electromagnet, which brakes the motion of the wheel to keep it constant. The system delivers 256 brakes per second, controlled by a samadium-cobalt electromagnet that has 25,000 coils.

The winding system is bi-directional and controlled by a lever that was developed in-house by Seiko in 1959. In the new 9RA5 movement, the Magic Lever, as it is known, is now off-set from its old placement at the centre of the movement, which means the caliber slims down. Two barrels power the movement, in differing sizes, and run in overlapping series so as to deliver a very even torque throughout the movement’s power reserve, while lasting for 120 hours.

In addition, a single piece bridge has been developed and machined, that’s meant to secure the new layout of the gear train, which means less parts and fewer screw points. But what’s great is that this single center bridge provides significant shock resistance for the movement, up to ISO 6425 requirements. On the back of the movement, in fact, you can just make out the two distinct barrels above the crown stem.

The new caliber is also more precise thanks to an improved integrated circuit that has a sensor to monitor the temperature of the movement. Since quartz, which is the oscillating stone that vibrates to deliver the regulating function of the electromechanical brake, is temperature sensitive, the circuit board compensates for any fluctuations in the oscillation rate.

The first watch to bear the new 9RA5 caliber is the Grand Seiko 60th Anniversary Limited Edition Professional Diver’s Watch 600M reference SLGA001, to be made available to customers in a limited edition of 700 pieces from August 2020 onwards. The movement offers a precision of 10 seconds per month, or 0.5 seconds a day.

The case and bracelet are in high intensity titanium, a Grand Seiko material that’s also seen in its 60th anniversary special editions. The material has double the hardness of steel while maintaining the light weight of titanium, along with a 600 meter water resistance and the movement is magnetically shielded, according to ISO 6425 requirements. The crown, like all Seiko diving watches, is screw-down and positioned at 4 o’clock, rather than 3, a Seiko characteristic. The bracelet also has an easy extension function for a convenient fit over a diving suit and a secure lock. Priced at €11,500, this is definitely a collector and diver’s must-have.