New: Grand Seiko T0 Constant-force Tourbillon – World Premiere For A Tourbillon With Co-axial Remontoir

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Press Release with commentary and technical insights in italics.

Grand Seiko T0 Constant-force Tourbillon

Ever since the first Grand Seiko was introduced in 1960, the pursuit for high accuracy has been fundamental in every Grand Seiko timepiece and innovation. Today, a new and exciting moment in its 60-year history is marked by the introduction of the brand’s first-ever concept creation.

The new creation is a masterwork and true revolution in watchmaking design and fully reveals the Grand Seiko designers’ capabilities and ingenuity.

The T0 (T-zero) Constant-force Tourbillon incorporates a fully integrated constant-force mechanism and tourbillon on the same axis for the first time in the world. The constant-force mechanism provides even energy distribution to the escapement regardless of how much the mainspring is wound, and the tourbillon eliminates the error in precision caused by gravity by incorporating the escapement parts and balance in a rotating carriage. These two mechanisms alone require exceptional design and manufacturing technologies, and the integration of the mechanisms as one unit is a patented design that achieves a new level of accuracy for Grand Seiko’s mechanical watchmaking.

In pursuit of the highest level of accuracy for mechanical watchmaking, the designers conceptualized the new creation without restrictions from production capability considerations. The free approach to development resulted in the birth of T0 and inspired essential movement parts for the new Caliber 9SA5, which was developed in parallel with the concept creation.

T0 is displayed on the second-floor lounge of the Grand Seiko Studio Shizukuishi inaugurated on July 20, 2020, in Shizukuishi, Morioka. The rotating tourbillon and intermittent turning of the constant-force as well as the rhythmical 16th note ticking sound of the mechanisms can be thoroughly enjoyed.

As soon as the Coronavirus situation allows, the new studio looks forward to welcoming visitors. For information and reservations, please visit the site below. URL:

IG Live Q&A with Joe Kirk of Grand Seiko USA, at his IG: @josep.kirk at 5pm EST, September 3, 2020 on this concept caliber.


This is not the first tourbillon made by Grand Seiko. Seiko had previously made the Fugaku under the Credor branding in their Morioka facility, which featured their first tourbillon. Read about that here. However this is the first time a remontoire constant force system is incorporated in any Seiko watch, and we believe, for that matter, any Japanese made watch. This is also not the first remontoir in a tourbillon. F.P. Journe achieved this milestone back in 1991 with his Souverain Tourbillon Remontoir d’Egalité. Journe has followed up with updates to this movement by making the entire movement in 18k rose gold and adding a seconde morte mechanism. The Arnold & Son Constant Force Tourbillon (2016) and the Andreas Strehler Tourbillon (2018) also features both these complications.

The most technically interesting aspect of the Grand Seiko T0 is perhaps the double cage design. As far as we know, this implementation of a double rotating carriage tourbillon with remontoir is unique. The Journe et al interpretations are all implemented on a single cage.

Double Cage – how does it work?

The outer cage is driven by the third wheel anchored around the fixed fourth wheel, and provides power to the carriage which is coaxially mounted within this outer cage. The connection between the outer cage and the tourbillon carriage is via the remontoir spring. This outer cage is blocked by a pallet stone attached to the inner carriage, meshing with the teeth of the ceramic stop wheel. During this blocked stage, the tourbillon carriage is driven entirely by the power of the remontoir spring, receiving a constant force energy source from the small spring discharging. As the carriage moves, it unlocks the pallet stone every 6 degrees of movement, allowing the remontoir spring to be recharged by the mainspring. It jumps in this recharge 6 degrees, before this motion is arrested by the next tooth in the stop wheel. The 6 degree rotational freedom corresponds to 1 second, and allows a seconds hand, if mounted on the outer carriage to execute its jump each second – the seconds morte.

Initial conclusions

The T0 also achieves impressive chronometry with a 50 hour power reserve during which the remontoir is running, providing a very impressive ±0.5s a day maximum deviation in their lab. This is quartz territory, though admittedly a standard quartz movement specification.

As we understand it, this is a concept movement, which is working and a kind of proof of concept. It remains to be seen how and when it will be implemented in a wristwatch. If we take the Fugaku experience, Seiko actually registered a patent for a tourbillon in 2000. The link to this patent is found here. But the Fugaku was only unveiled in 2016.  

Quite interesting. We are keen to inspect the actual movement ourselves, but with the current travel restricted situation, and the model only being available in Japan, we figure it won’t be anytime soon.



    • Thanks Jeff. Perhaps I should have been more precise in saying that a coxially mounted remontoir on a double cage tourbillon…but I am not sure if that’s a good way to describe the mechanism – a double cage tourbillon.