Grand Seiko 9R Spring Drive and the pursuit of a long power reserve.

A mechanical watch’s power comes from its mainspring. Once all the power has been depleted and the mainspring is unwound, the watch stops. In the 1990s, the power reserve of a typical mechanical watch was around 40 to 50 hours.

Like a mechanical movement, Spring Drive is also powered by a mainspring. In 1999, when the first Spring Drive watch was released, its power reserve stood at 48 hours, a figure in line with contemporary mechanical watches. But when developing Caliber 9R, Grand Seiko pursued a longer duration of 72 hours.

Spring Drive generates electricity from the unwinding of a mainspring, and an electromagnetic brake controls the speed at which the glide wheel at the end of the gear train turns. The Spring Drive movement necessitated the creation of a low-power IC to guarantee a long enough power reserve for a practical watch. This critical feature evaded engineers during the technology’s first and second stages of development in the 1980s and ‘90s. Finally, they overcame the challenge during the third development stage, and a watch with a 48-hour power reserve was launched in 1999.

By the 2000s, 72 hours of power reserve represented a new high bar for Spring Drive. In 2004, Grand Seiko achieved it with the Caliber 9R65, which combined a long duration with the convenience of automatic winding while displaying the hours, minutes, seconds, and date. While developing the flagship 9R automatic movement, the team already had its sights on creating another movement that would achieve a 72-hour power reserve even with a chronograph, a power-draining feature, in operation.

In addition to developing an IC using SOI (Silicon on Insulator) for low power consumption (about 1/100th of that of the first Spring Drive development stage), the team also pursued a long power reserve through various other methods. These included polished pinions, enhancements to the coils for power generation, and using a specific material to reduce energy lost to magnetism. Techniques and expertise acquired in mechanical watches such as the Grand Seiko First and the 61GS, as well as others learned in quartz and semi-conductor technology used for 9F quartz, were combined in pursuit of a longer power reserve.

The latest generation of 9R Spring Drive movements is the 9RA series, which comprises the Calibers 9RA5 and 9RA2, developed in 2020 and 2021, respectively. These movements combine automatic winding with a long power reserve of 120 hours, or five days, leading to a new level of performance and convenience. Their ample power reserves were achieved through the use of two ingeniously engineered barrels. While two barrels are not unheard of in watchmaking, they are typically the same approximate size, leading to unused space in the movement. The Dual-size barrels of 9RA2 and 9RA5, by contrast, have a smaller footprint, making the most of the available room and allowing for a compact movement design. One barrel is small and thick, while the other is larger and thinner. Each of the two mainsprings is designed to wind and unwind in a way that maximizes the power reserve created through their combined output.

The watchmaking skills of a vertically integrated manufacture lie at the heart of such innovations. The barrels, gear trains, crystal oscillators, and ICs used in the 9RA movement series are all produced in-house. And Grand Seiko designs, manufactures, and assembles all of its major components, creating highly efficient movements capable of running for long periods of time.