06 Aug Grand Seiko’s newest Caliber: 9RB2 Ultra Fine Accuracy (UFA)
A new era of accuracy from Grand Seiko – Caliber 9RB2 – Ultra Fine Accuracy (U.F.A.)
The Caliber 9RB2 introduces the Ultra Fine Accuracy (U.F.A.) designation, achieving an extraordinary annual precision of ±20 seconds—the most accurate mainspring-powered movement ever created (as of April 2025, based on Grand Seiko’s research). This exceptional performance is made possible by an aged quartz oscillator, a newly developed integrated circuit, and a vacuum-sealed regulation system that ensures long-term stability. With a 72-hour power reserve and 34-jewel construction, 9RB2 embodies Grand Seiko’s relentless pursuit of innovation and precision.
The new movement achieves its ±20-seconds-per-year accuracy thanks to new and enhanced manufacturing and processing methods for the three-month-aged quartz oscillator, and a newly designed IC. And, as with the 9RA series of Spring Drive movements, the frequency of each individual quartz oscillator is measured at several different temperatures, with the resulting data necessary for thermo-compensation programmed into the low-power IC. Both the oscillator and sensor are vacuum-sealed to minimize temperature differences and protect against external factors such as humidity, static electricity, and light, ensuring precise temperature adjustments and the stable performance of the quartz oscillator. In addition, 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 occur over long periods of use.
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.
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.