Spring Drive U.F.A.
Caliber 9RB2
The pursuit of high accuracy has always been the cornerstone of Grand Seiko’s values. Receiving the new U.F.A. designation, which stands for “Ultra Fine Accuracy,” Caliber 9RB2 boasts a level of precision defined not by accuracy in seconds per day, week, or month, but by accuracy over one year. The movement has an astounding annual rate of ±20 seconds, or approximately ±3 seconds per month, setting a new standard among wristwatch movements powered by a mainspring*.
*As of April 2025, based on Grand Seiko’s research.
Spring Drive utilizes the properties of a crystal that vibrates at a constant frequency to measure the passage of time. When external factors such as temperature changes, humidity, and gravity are applied to the crystal oscillator, the frequency changes, resulting in tiny errors. Over time, they may cause the accuracy to deviate slightly.
The±20-seconds-per-year accuracy of Caliber 9RB2 is achieved by thoroughly reconsidering the manufacturing and processing methods for the in-house, three-month-aged quartz oscillator and a newly designed temperature-compensating IC. Furthermore, by incorporating a newly developed regulator switch, accuracy deviation due to aging after assembly is minimized more than ever before.
Specifications
| Winding mechanism | Automatic with manual winding |
|---|---|
| Accuracy | ±20 seconds per year (±3 second per month) |
| Power reserve | Approximately 72 hours (3 days) |
| Number of jewels | 34 jewels |
| Features | -Offset Magic Lever
-One-piece Center Bridge -Power-reserve indicator -Date display |
A vacuum-sealed package consisting of a carefully selected crystal oscillator
As with the 9RA series of movements, Caliber 9RB2 relies on a three-month aging process for its quartz oscillators and a temperature-compensating ultra-low-power IC, in which both the oscillator and sensor are vacuum-sealed to minimize temperature differences. The frequency of each individual quartz oscillator is measured at several different temperatures after the movement is cased up into the watch, with the resulting data necessary for thermo-compensation programmed into the low-power IC. The oscillation of a crystal oscillator is susceptible to temperature fluctuations, so Caliber 9RB2 utilizes a temperature sensor located within its special silicon-on-insulator IC (SOI-IC) to collect temperature data 540 times daily, determine the influence of temperature changes within the IC, and compensate for variations in the oscillator’s performance. Furthermore, placing both the crystal oscillator and the IC within a single, vacuum-sealed package eliminates temperature differences between the IC and the crystal oscillator, allowing for highly precise temperature adjustments. Installing all wiring connecting the crystal oscillator with the IC within the vacuum-sealed package also prevents changes in humidity from influencing the movement in addition to shielding the IC from the influence of static electricity and light.
The first-ever regulation switch for Spring Drive
Additionally, by understanding the characteristics caused by the slight strain that remains after the crystals are artificially aged in house, it became possible to compensate for subtle deviations in vibration frequency with future aging. For the first time in Spring Drive, the new movement features a regulation switch that can be used during after-sales service to correct any divergences in accuracy that may be caused over long periods of use.
Achieving high accuracy and a compact design
To create a movement with a low center of gravity, which in turn enhances the comfort of the watch, a thin single barrel and a new Magic Lever with crank wheel, which is offset from the center of the movement, were developed. The movement maintains its low center of gravity while simultaneously ensuring a power reserve of approximately 72 hours, and just like the 9RA series, its robustness is ensured by the “One-piece Center Bridge” structure. Thanks to the movement’s thin profile and small diameter, the smallest models powered by the 9R series have been created, with a case diameter of just 37mm.
Movement finishing reflecting the natural beauty of Shinshu
The exterior of Caliber 9RB2 is meticulously finished and reflects the natural beauty of its birthplace, Shinshu, an area more commonly known today as Nagano Prefecture. The design itself draws inspiration from the gentle frost that covers the trees during the severe winters of this mountainous region. An eye-catching feature of these frosts is the hypnotic, all-encompassing glow emitted from the layer of frost due to its peculiar, rugged texture. The movement’s bridge design represents the frost and is finished with a neutral-toned sandblast coating that achieves a calm but elegant radiance. The edges of the bridge emit a sharp glow with light captured from any direction accenting the design with a vivid and profound brilliance. The oscillating weight is designed with the engraving "Ultra Fine Accuracy" to make it instantly identifiable as having the U.F.A. designation.
