IN JAPAN, watch enthusiasts often refer to Grand Seiko as “saiko no futsuu” (最高の普通), which roughly translates to “the best of normal”. The 45GS (Grand Seiko) and the 45KS (King Seiko) is a prime example of a seemingly normal watch but at a closer look, a watch packed with historical and technical significance. Both watches employ the legendary caliber 45 family of movements – arguably the greatest movement made by Seiko.

Introduced by the Daini Seikosha in 1968, the Hi-Beat caliber 45 was used in both the King Seiko and Grand Seiko models, and is loved by Seiko enthusiasts around the world for its incredible accuracy.

There were namely two reasons why this movement is so accurate even in today’s standards. One is the large balance wheel (the balance wheel of a hi beat movement is usually smaller than a low beat movement). The second reason is because of the thick and powerful main spring. Despite the balance wheel and main spring being large, the engineers at Daini were still able to make a thin movement by employing a unique layout of the gear trains. Specifically, the 2nd gear wheel was moved off center and instead the 4th gear wheel was positioned there.

The 4500

Caliber 45 was a completely new design for Daini. Certain concepts were carried over from the 44KS, such as being manually wound to provide a lower profile, and having a more stable balance bridge secured at both ends rather than a balance cock secured at just one. In most other aspects however, the movement was all new. It was produced in five versions:

• the base no-date 4500 movement 
• the 4502 with a newly developed instant date change mechanism
• the higher grade 4520 used in the Grand Seiko 45GS
• a higher grade 4522 with the same instant date change mechanism
• An even higher grader 4580 used in the rare Grand Seiko 45GS VFA (Very Fine Adjusted)

As well as running at twice the rate of the earlier 44KS, the 45KS gear train was also unconventional. The barrel drives a tiny center wheel, an intermediate wheel and a large off-center driving wheel combination. This then drives the third, fourth and escape wheels. The second hand is then driven by another center wheel driven indirectly from the second wheel. Drive is transferred to the dial via a cannon pinion attached to the tiny center wheel deep inside the movement.

An ‘indirectly-driven’ wheel is one driven by a wheel in the train but it itself is not part of the train because it does not transmit power in to a neighboring wheel. A ‘directly-driven’ wheel is one the is part of the train because it is both driven by the previous wheel and also transmits power to the next wheel in the train.  A directly-driven wheel in the train will always have torque acting up on it from the main spring even when the train is locked by the escapement. An indirectly-driven wheel only receives torque when the train is unlocked and moving. 

In the 45KS movement above, we can see that the uppermost center wheel [1] is driven by a pinion on the the second wheel [2] but it does not mesh with any other wheel and so is indirectly-driven. The lack of permanent torque on this center wheel can be seen as a slight wobble or shimmy on the otherwise smooth high-beat sweep of the 45KS second hand. 

The need for the unconventional and somewhat complex going train was perhaps necessitated by the extra strong mainsprings Daini fitted to these movements to drive the balance at 36000 vph. Most high beat movements have small balance wheels but for the 45KS, Daini fitted a relatively large balance wheel that required a lot of torque to gain the amplitude required.