Monochrome Watches
An online magazine dedicated to fine watches

The Grand Seiko T0 Constant-Force Tourbillon, the Brand’s First Tourbillon with a World-First Remontoire Device

When Grand Seiko goes not only high-end, but also super-technical!

| By Brice Goulard | 7 min read |

Today, we’re not going to talk about watches. We’re going to talk about watchmaking, in the purest sense of the word. Today, it’s all about a movement, not yet a timepiece – this will certainly come in a few weeks/months. And what a movement it is. Today, Grand Seiko climbs up the complications ladder with a leap as it introduces the Grand Seiko T0 Constant-Force Tourbillon, which is the brand’s first-ever tourbillon movement equipped with a world-first constant force mechanism. Quite something, indeed.

When you think Grand Seiko, you might think robust, finely executed automatic calibres or even hi-beat movements. Altogether, nothing to complain about – at all – as the idea was to provide solid specifications and reliability on a daily basis. Fine watchmaking, for sure, but not high horology. In a way, Grand Seiko is (was…) the Japanese equivalent of Rolex or Omega. However, recently, the brand demonstrated that it might have a couple of new tricks in its bag of innovations, with the introduction of the calibre 9SA5 with the Dual Impulse Escapement, an innovative new geometry of the escapement that greatly differs from the classic lever escapement (used by approx. 99% of the mechanical watches). We knew the brand was able to introduce a fair dose of innovation, but today’s announcement takes it to yet another level.

The Credor Fugaku was, in 2016, the first tourbillon watch ever created by the Seiko conglomerate. Still, it was traditionally built, with classic technical solutions.

Within the Seiko conglomerate – which includes Seiko, Grand Seiko, Credor, Orient and Pulsar – there had already been tourbillon movements in the past, under the high-end brand Credor. Launched in 2016, the Credor Fugaku Tourbillon was a very… original watch (to put it mildly), with highly decorated dial and stones. The movement, equipped with a tourbillon, was true high horology visually speaking but remained technically classic.

Ad – Scroll to continue with article

In 2020, Grand Seiko continues its pursuit for high accuracy, not only with the impressive Dual Impulse Escapement but now with a brand new tourbillon movement. What’s new about that, you’d ask? Well, THE impressive part isn’t really the tourbillon, but the constant force mechanism linked to it. First, constant force devices are rare and considered the pinnacle of true horology (understand accuracy). Second, this is the first time Grand Seiko develops a tourbillon watch. Last but not least, the combination of a tourbillon and a constant force mechanism is sort of a dream machine for high-end watchmaking, and Grand Seiko has developed something unprecedented.

Technically advanced… and very, very good looking too!

The goal of the tourbillon is to counteract the effect of gravity on the regulating organ. Invented by A.L. Breguet and patented in 1801, the solution was to enclose the balance and escapement in a cage rotating on itself, thus negating the force applied by gravity on crucial parts of the movement, as these parts are in constant motion. This device has become a must-have for chronometry contests. But… this isn’t enough, as other problematic forces apply on a mechanical movement, mostly the variation of the torque of the mainspring. The mainspring, as any spring, tends to provide more torque when fully wound than when it is almost unwound. This varying delivery of torque to the rest of the movement, understand the escapement, will have an effect on the amplitude of the balance and thus on its precision.

To counteract this problem, watchmakers have invented so-called constant force devices, among which is the fusée-and-chain or the remontoire d’égalité – read our in-depth article on constant force devices here. A remontoire is a secondary spring (a blade or coiled spring) to power the escapement. It is rewound periodically by the mainspring and isolates the escapement and oscillator from the varying torque of the barrel. This is the solution used by Grand Seiko, however, not in the usual way, as for instance F.P. Journe, with a remontoire positioned in between the escapement and the gear train.

First of all, the new Grand Seiko T0 Constant-Force Tourbillon relies on a double-barrel architecture, already renowned for its more stable delivery of torque – at equal power reserve, two smaller springs are less prone to a varying torque than one large spring. Here they are positioned in parallel, so torque will be doubled (the idea isn’t to prolong the power reserve but to enhance the delivery of energy). But beauty lies in the cage at 6 o’clock. For the first time ever, a movement incorporates a fully integrated constant force mechanism and tourbillon on the same axis.

One thing to understand is that when a constant force device is placed close to a mainspring, it is easier to control the unwinding power of the mainspring. However, efficiency is lower and torque is uneven because it is relatively removed from the balance. On the other hand, when placed closer to a balance, it is able to deliver a stable release of energy to the balance. In this case, torque has to be controlled to a very small amount as it comes closer to the balance wheel, making it hard to keep the stability.

Takuma Kawauchiya, a movement designer and watchmaker of Seiko Instruments Inc., has developed a stable system while placing constant force as close to the balance as possible – in fact, on top of the balance, inside the tourbillon cage (watch the video to see it in action). Usually, the tourbillon carriage incorporates a balance and an escapement mounted on the fourth wheel that rotates once per minute. In most cases, when a constant force device is added, it is placed away from the carriage – the remontoire is usually placed next to the tourbillon, in order to provide greater control of the energy delivered.

The Grand Seiko T0 Constant-Force Tourbillon stores torque from a coaxially arranged gear with the carriage in a constant force spring and the energy of the unwinding spring is used for rotating the carriage including the balance in it.

Other improvements have been made too, such as the central and third wheels treated with a special coating to reduce friction to accommodate the great torque generated by the twin barrels. Also, the tourbillon beats at 4Hz, faster than most of the tourbillon on the market (often at 3Hz), in order to provide greater accuracy. This linked to a free-sprung balance without a regulator. The mechanism adjusts to the gaining and losing of time through the inertia of the balance, without changing the length of a hairspring. A measurement test using a prototype found that the impact of gravity was reduced to one-tenth or less thanks to the tourbillion, and high accuracy was maintained for 50 hours out of 72 hours due to the constant force. The high frequency and a free-sprung balance would significantly increase the accuracy when wearing a watch.

The Grand Seiko T0 Constant-Force Tourbillon also integrates a hacking function. However, it is difficult to add a hacking function to a tourbillon whose movement is constantly rotating. Kawauchiya decided to stop the carriage itself instead of the sole balance. T0 is then designed to facilitate a restart by rotating a carriage instantly in the opposite direction when a lever for stopping the carriage comes off (patent pending).

Finally, the movement is fully opened, revealing all its parts and decorated in a modern yet high-end way. It displays the hours and minutes at 12 o’clock, a small seconds on the tourbillon cage and a power reserve at 8 o’clock. Now comes the question regarding feasibility and its arrival on the market. For the time being, the movement is displayed on the second-floor lounge of the Grand Seiko Studio Shizukuishi inaugurated on July 20, 2020, in Shizukuishi, Morioka. Still, it would be a shame not to see this calibre ticking in a wristwatch soon… No words on that yet, but we’d be very happy to see this in the metal.

More details at

3 responses

  1. Somebody please tell me what the annotation on the back of the movement “16th note feel” means?

Leave a Reply