The Ultra-High Precision of 9R Spring Drive

Precision is paramount in every Grand Seiko wristwatch, and it has always been this way. This is true whether the movement is mechanical, quartz, or Spring Drive.

The team responsible for the first Grand Seiko aimed to make the best watch of which they were capable. Naturally, they pursued high precision as a crucial objective in their mission to create an ideal watch for everyday wear.

No less ambitious was the dream that led to Spring Drive: the determination to create a mainspring-powered movement capable of providing the accuracy of an electronic timekeeper. Looking back, the development of Spring Drive was pivotal in watchmaking history, and it has played a major part in the trajectory of Grand Seiko. Spring Drive is more than 10 times as accurate as a mechanical watch that uses a traditional balance, yet elements of Spring Drive’s architecture – a mainspring, a gear train, finished bridges, and an oscillating mass – would likely be familiar to a classically trained watchmaker from a previous era.

Even before 9R Spring Drive, Grand Seiko pursued accuracy, legibility, beauty, and durability in its watches. In developing 9R Spring Drive, Grand Seiko envisioned a future for watchmaking in which tradition and innovation would coexist. There was an inherent duality to this vision. A movement powered by a conventional mainspring, but with accuracy controlled by a super high-precision IC and crystal oscillator, represented opposite ends of the horological spectrum. Yet in Spring Drive, their integration resulted in a unique and attractive product that could only be achieved through a mastery of all types of watchmaking.

The integrated circuits and crystal oscillators used in Spring Drive are developed and manufactured in-house at Seiko Epson and creating them is a challenge. Because there is no battery, only a spring, these parts must be sparing in their use of power. No matter how accurate the Spring Drive mechanism is, if the IC drains power too quickly, the watch will not have the practical power reserve expected of a Grand Seiko. In Caliber 9R65, the first Grand Seiko Spring Drive movement, the IC’s power consumption is as little as 25nW, one percent of what the prototype sample made in the first development phase in the 1980s consumed. Thanks to the 72-hour power reserve allowed by this IC, Spring Drive was finally ready to power a Grand Seiko watch in 2004.

Grand Seiko 9R Spring Drive overcomes virtually all of the most common challenges faced by purely mechanical watches – namely their susceptibility to the influences of temperature, position, and shock. Moreover, in conventional mechanical watches, a change in the amount of torque as the mainspring winds down results in variability in the amplitude of the balance, affecting accuracy. By contrast, Spring Drive maintains its high level of accuracy for the whole period of the power reserve – 72 hours in the case of 9R65.

In the years since the development of Caliber 9R65, with its accuracy of ±15 seconds per month, even more highly accurate 9R Spring Drive movements have been introduced with precision to ±10 seconds. These were previously limited to the Caliber 9R01 from the Micro Artist Studio, as well as specially adjusted movements such as 9R15, 9R16, and 9R96.

A new IC developed for the 9RA series of movements, which debuted in 2020, also allows an accuracy of ±10 seconds per month. This new IC is equipped with a temperature sensor, and it consumes more power than the IC used in 9R65. To mitigate the increase in power consumption, a new circuit design and manufacturing process were instituted. Placing the IC and a 90-day aged crystal in a single vacuum-sealed package eliminates temperature differences between the temperature sensor and crystal oscillator, allowing for highly precise temperature adjustments. Further, this construction prevents other external influences such as static electricity, humidity, or light from affecting accuracy.

These parts do their amazing work largely hidden from view, discreetly tucked beneath a finely finished movement bridge. In other 9R movements, the IC and crystal are completely hidden. To own and wear a Caliber 9R Spring Drive watch is to encounter the beauty and complexity long prized in traditional mechanical watches, and much, much more.