Grand Seiko

Introducing the Grand Seiko T0 (T-Zero) Constant-Force Tourbillon

Grand Seiko

Introducing the Grand Seiko T0 (T-Zero) Constant-Force Tourbillon


Respect for nature informs the overall themes of Grand Seiko, from subtle dial designs to the sublime architecture of the new headquarters in Shizukuishi, Japan. Innovation and respect for the past are at its core, which is why the latest innovation, the T0 (T-Zero) Constant-force Tourbillon, is so remarkable, a technical feat that attempts to defy nature with a world’s first mechanism.  Gravity affects the capabilities of all movements, especially in the pursuit of a high accuracy timepiece, the T0 attempts stand up to all that. To say Grand Seiko has made great strides this year on behalf of their 60-year history would be quite the understatement.

Read more about the history of Grand Seiko, here.

A masterwork of the Grand Seiko designers’ inventiveness, the T0 combines a fully integrated constant force mechanism (a.k.a. remontoire) and tourbillon on the same axis for the very first time. The Grand Seiko Studio Shizukuishi was allowed to dream without the constraints of considering production capabilities, bringing about the T0 Constant-force Tourbillon concept while inspiring essential parts of the Caliber 9SA5, the high-accuracy, long-lasting performance movement released earlier this year. Developed simultaneously in secret, the all-consuming process allowed for the conception of two entirely new movements designed entirely from the ground up.

So why is this T0 Constant-force Tourbillon so significant? Let’s try to break it down.

Mechanical watches get their power from the unwinding force of a mainspring. This mainspring slowly loses energy as it unwinds. This accuracy has improved for extended hours due to advancements in watchmaking (i.e., Grand Seiko’s Calibre 9SA5). Ideally, torque (the twisting force that causes rotation) should be the same fully wound or unwound. Keeping torque stable is vital for maintaining timepiece accuracy. The constant force mechanism of the T0 is a groundbreaking way to ensure the stability of this torque.

When constant force gets placed close to a mainspring, the mainspring’s unwinding power is easier to control. However, the torque becomes irregular, and the efficiency of the watch becomes uneven. If it’s placed closer to the balance, energy becomes more stable, but the torque is harder to control—a delicate trade-off, nearly impossible to have it both ways. Here a stable system was developed, placing the constant force as close to the balance as possible. This is the part where gravity comes into play with the addition of the tourbillon.

T0 Constant-force Tourbillon movement broken down into its minuscule parts

In general, a tourbillon carriage incorporates a balance, and an escapement mounted on a fourth wheel that rotates once per minute. The T0 stores torque from a gear coaxially arranged with the carriage in a constant force spring, and the energy of the unwinding spring gets used for rotating the carriage, including the balance in it. Twin barrels are placed here in parallel, doubling the torque– the first movement in Seiko’s history of watchmaking to have two barrels placed parallel to release the stable constant force mechanism.

Additional improvements were added based on mechanical achievements from earlier innovations like the Calibre 9S65– the mainspring, wheel trains, escapement, balance, setting lever, and yoke. The 9SA5 provided a free-sprung balance with a regulator and high beat technology boasting 28,800 vibrations/hour.  A prototype tested revealed that gravity’s impact was reduced to one-tenth or less due to the tourbillon, and high-accuracy was maintained for 50 hours out of 72 hours due to the constant force. The combination of high frequency with a free-sprung balance would significantly increase the accuracy when wearing a watch – the T0 backs this up with a real movement.

A side view of the Grand Seiko T0 (T-Zero) Constant-Force Tourbillon

Taking more than three months to produce, the T0 uses a fascinating manufacturing process called the Micro Electro Mechanical Systems (MEMS) to create gears. In this process, metal films are layered like plating to create perfect gear shapes measured in microns. Additional components like the main plate and bridges get painstakingly finished by hand. The ticking sound of the watch is also unique. A watch that has 28,800 vibrations/hour ticks eight times per second– the T0 adds the impact sound of the constant-force every second with a ceramic stop wheel (an example of which can be heard in the Grand Seiko video).
A concept fully released in September of 2020, a five-year creation representing the world’s first movement with a fully integrated constant-force and tourbillon on the same axis, attempting to create a mechanical watch with the highest accuracy possible. While the Constant-force tourbillon might only be a concept viewable at the Grand Seiko Studio Shizukuishi, the ground-breaking movement has applications to be applied to all Grand Seiko mechanical marvels yet to come. Who knows, by the time the world returns to travel and trade shows I’d be willing to bet we’ll see a commercialized version. After witnessing Grand Seiko’s achievements for this year alone, I wouldn’t be surprised in the slightest.

The back of the Grand Seiko T0 (T-Zero) Constant-Force Tourbillon movement