Astonishing accuracy in a spring-powered watch
Grand Seiko Spring Drive U.F.A.

In 2025, Grand Seiko reached a new pinnacle. By further advancing Spring Drive, a unique movement technology with a spring providing motive power and speed governed by a crystal oscillator and IC chip, it achieved an astonishing accuracy of ±20 seconds per year. This is what the new Caliber 9RB2, Grand Seiko’s Spring Drive U.F.A. movement, is all about. How was this great achievement accomplished? Here, we delve into not only the secrets behind the developments that made this innovation possible but also the watch’s overall structure and design.

The history of Spring Drive, born of Grand Seiko’s constant pursuit of accuracy

Spring Drive is a radically unique movement merging the advantages of mechanical and quartz technologies. Where it stands apart is in achieving both the strength of mechanical watches and the accuracy of quartz watches. The history of Spring Drive began in the latter part of the 1970s when a Seiko Epson designer came up with the concept of “a quartz watch driven by a mainspring.” One issue to be overcome was energy efficiency so that electrical energy sufficient for driving the crystal oscillator (quartz) could be obtained from the unwinding force of the mainspring alone. After approximately 20 years of development from the initial concept, a model was announced in 1999 that was built on Caliber 7R68, the first-generation Spring Drive movement.(*) Even while using a mainspring as its power source, its operation was controlled by a crystal oscillator and integrated circuit (IC); besides having long, thick hands like those of a mechanical watch, it was accurate to ±15 seconds per month, setting it apart from any previous wristwatch.

Besides its achievement of high accuracy in a spring-driven movement, Spring Drive brought other advantages. In addition to the accuracy remaining unchanged even when the position of the wristwatch changes, the absence of an escapement causing friction made the watch highly resistant to shock and resulted in the smooth motion of the hands. Spring Drive, in other words, with its high accuracy and originality, is very much a mechanism fit for a Grand Seiko. That is why, since 2004, Grand Seiko watches have adopted this innovative timekeeping technology. With the birth of Caliber 9R65 in 2004, which extended the power reserve to around 72 hours, Spring Drive became even more practical. In 2020, Caliber 9RA appeared, achieving both higher accuracy and a longer power reserve. Not only did the high-efficiency Dual-size Barrels enable the movement to realize a power reserve of approximately five days, but the movement also came with an IC temperature correction function for greater accuracy, among other advances.

*The Caliber 7R68 model announced in 1999 as the first-generation Spring Drive was released under the Seiko brand.

The Spring Drive mechanism

Spring Drive is an original driving mechanism that, while using a mainspring as the power source, combines it with the high accuracy of quartz control. The main feature is the Tri-Synchro Regulator. Having a mainspring as its power source is the same as a mechanical watch, but Spring Drive is different in that there is no escapement, a part normally found in a mechanical watch. Instead, an electromagnetic brake is applied to the glide wheel, which is driven by the mainspring as it unwinds, generating electrical energy; and this electrical energy is used for integrated circuit (IC) control and to activate a crystal oscillator. This is the reason for the smooth movement of the hands and why high accuracy, difficult in a mechanical watch, was achieved.

Among the Spring Drive movements currently used in Grand Seiko watches, Caliber 9R65 is positioned as the mainstay Grand Seiko Spring Drive movement. Its sturdiness and high accuracy, along with its three-day power reserve, have made it the movement of choice for many models. Further advancing these advantages is the Caliber 9RA series, which can be found in several models in the Evolution 9 Collection. To realize the necessary power reserve and high torque in such a limited movement space, the original Dual-size Barrel structure was adopted, equipped with two barrels of different sizes, large and small, extending the power reserve to approximately five days. A temperature correction function was also added for improved accuracy.

Spring Drive Caliber 9RB2 with remarkable annual accuracy of ±20 seconds debuts in the forward-looking Evolution 9 Collection

Grand Seiko Spring Drive has made major advances since its debut. The movement that can be seen as the culmination of this progress is the Spring Drive U.F.A. announced in 2025. A central feature of this movement is its high accuracy, which surpasses that of any spring-driven to date. It is the first Spring Drive movement to express its accuracy not in seconds per month, but per year, with an annual variation of ±20 seconds, the most accurate of a spring-driven mass-production movement. (*)

The crystal oscillator at the heart of Spring Drive is, after all, far more accurate than the escapement in a mechanical watch. As with other movements, though, it is subject to error from changes in temperature and humidity. Grand Seiko had already adopted a temperature-correction function in the Caliber 9F series quartz movement, but adding this function to Spring Drive, with its comparatively small electrical energy, was more of a challenge. With Caliber 9RA2, however, Grand Seiko succeeded in adding a temperature correction function and a vacuum package IC for stabilizing accuracy. The accuracy of Spring Drive was improved from ±15 seconds to ±10 seconds per month.

Still, this was not enough to achieve a movement with annual accuracy. Here the movement design team, led by Seiko Epson’s Eiichi Hiraya, added a function to adjust for slight lags or advances in long-term use that affect accuracy, while also subjecting each part, including the crystal oscillator, to a thoroughgoing review, addressing each of the factors that can impact accuracy over time. In addition, while maintaining the same 30 mm movement diameter as Caliber 9R65, in place of the magnetic shield plate for shutting out magnetism, they heightened the magnetic resistance of the movement itself, thereby achieving a compact case size of 37 mm for the first time in a Grand Seiko Spring Drive. The name of this movement is Spring Drive U.F.A. (Ultra Fine Accuracy). It harkens back to 1969 when the V.F.A. (Very Fine Adjusted) model realized the highest accuracy to date in a mass-produced mechanical watch. The Spring Drive U.F.A., while carrying on with that spirit, can be seen as testimony to having arrived beyond that accomplishment, using today’s technology.

*As of April 2025. Internal research.

Two examples of the ingenuity behind the high accuracy of Caliber 9RB2

Advancing toward further accuracy, compactness, and thinness

Major features of Spring Drive U.F.A. are its accuracy of ±20 seconds per year and the new case size of 37 mm diameter. These features represent an advancement worthy of chronicling in the history of Grand Seiko, but the compact 37 mm diameter case is not simply a size reduction. The performance, design, and wearing comfort are all the result of a reconfiguration.

Pivotal to this is the Caliber 9RB2 movement adopted in these models. The magnetic shield plate aimed at magnetic resistance in Spring Drive models up to now has been eliminated. In its place, a magnetic resistance component is embedded in the movement itself, gaining greater exterior design freedom as a result. This made it possible to keep the new movement to the same compact, 30mm size as Caliber 9R65. The design philosophy behind these models, the Evolution 9 Style, ensures high legibility through the use of long, thick hands and three-dimensional indexes, along with excellent wearing comfort thanks to the low center of gravity of the case design.

While earlier models went with a 40 mm size, the new models are more compact at 37 mm in diameter. The style design follows the same Evolution 9 Style design code, but the form has undergone an overall revamp in slimming down to a smaller size.

The Evolution 9 design philosophy of legibility, comfort, and timeless aesthetics

The way nature changes its expressions through the passing of the seasons has long influenced the Japanese aesthetic, to which Grand Seiko pays homage. The dial pattern on these models expresses the beauty of soft rime, on trees in a clear snowfield in the Shinshu region, where the Spring Drive is made.

What’s more, the “dial expressing soft rime” symbolizes the silently gliding hands of Spring Drive. The designer, Akira Yoshida, has incorporated in the dial both the stately rows of trees covered in snow and ice and the motion of the silently driven Spring Drive seconds hand.

The task of incorporating soft rime on a watch dial was never going to be an easy one. If the dial pattern were too small, it would be hard to recognize it as soft rime, whereas a large dial pattern would cover the indexes, to the detriment of legibility. Today’s Grand Seiko, however, can match an irregular pattern to the dial. The pattern is applied to the dial by stamping; and by adjusting the plating and other coloration on that pattern, a dial that is unique but still true to the Grand Seiko insistence on legibility has been achieved.

The dial finish has, moreover, been customized to each of the case materials. For the SLGB003 with its titanium case, a silvery blue tint has been chosen. The dial color is in harmony with the lightness of the case. As for the SLGB001 and its platinum case, the dial is given a very slight bluish tint that befits the platinum material with its clear hue. Even so, this coloration is done subtly, just barely noticeable, so as not to stray from the soft rime concept. Adding clear and subtle coloration is also a Grand Seiko specialty.

Innovations in the clasp further improve wearing comfort. With the SLGB003 and its high-intensity titanium case, the clasp features a mechanism for making fine adjustments. Since the length can be adjusted readily without specialized tools, a more excellent wearing comfort can be obtained. The size, too, has been made more compact without sacrificing any of the sturdiness for which Grand Seiko is known.

A new direction for Grand Seiko

Spring Drive U.F.A. boasts an accuracy of ±20 seconds per year, which is the pinnacle of accuracy not only in the history of the Spring Drive but for any mainspring-driven wristwatch. The SLGB001 and SLGB003 models, moreover, succeed in housing this in a 37 mm diameter case size. Even with the smaller case, they remain faithful to the Evolution 9 Style. The SLGB003 has further improved wearing comfort with a fine-adjustable buckle and lightweight High-Intensity Titanium exterior.

The SLGB001 and SLGB003, while carrying on the Grand Seiko virtues and further redefining them, are models that indicate a new direction not only for the Spring Drive but for Grand Seiko itself.

Photographs by Eiichi Okuyama
Text by Masayuki Hirota (Editor-in-Chief of Chronos Japan Edition)