In many cultures in East Asia the 60th birthday signifies new beginnings, a moment of rebirth. The Japanese embrace the tradition of Kanreki, which literally means your years completed in a circle and symbolizes a return to the time you were born. Grand Seiko turns 60 this year and boy, they have taken this reinvention business very seriously indeed.

The Caliber 9SA5 used in the Grand Seiko SLGH002

After introducing a new escapement which riffs on the direct impulse escapement (Ref. SLGH002) earlier this year, Grand Seiko today unveiled a concept constant-force tourbillon movement it calls the T0 (that’s tee-zero). This isn’t the first tourbillon from the House of Seiko - that would be the Credor Fugaku tourbillon from 2016. Neither is this the first wristwatch to combine a rementoire (a constant force mechanism) and a tourbillon, but this is a first for Grand Seiko and the brand claims that this is the only time a rementoire and a tourbillon have been brought together on the same axis.

In a sense, this is a continuation of Grand Seiko’s original pursuit of creating the most accurate wristwatch. Back in 1960, Grand Seiko was born out of Seiko’s quest to create “the ideal watch” – a beautifully handcrafted timepiece that would be durable, legible and with higher chronometric standards than Swiss watches. By the end of the decade, their mechanical movements had swept the top spots at chronometry competitions held by the Neuchatel and Geneva Observatories.

The rementoire seen on the Richard Lange Jumping Seconds

Before we go any further – a quick primer on these two haute horology mechanisms. The remontoire (or remetoire d’égalité) is a spiral spring placed on one of the gear train wheels to ensure that the escapement gets a constant supply of power as long as there’s juice in the mainspring barrel. This helps keep the amplitude of the balance spring constant for precision timekeeping. A tourbillon works on the principle that if the balance is in constant rotation, the effects of gravity on the accuracy of the movement can be negated. In effect both these mechanisms, extremely hard to engineer and assemble, serve in the interest of accurate timekeeping. The Tourbillon Souverain from F.P. Journe in 1999 was the first wristwatch to bring together these two devices.

The three-armed blued titanium arms work for two carriages

According to Grand Seiko, the product development team that worked on creating the Caliber 9SA5 used in the SLGH002 worked simultaneously on the T0 constant-force tourbillon as well. The movement was designed by Takuma Kawauchiya. While in most arrangements, the rementoire is placed away from the escapement because it’s easier to control the torque from the mainspring, Kawauchiya found that this wasn’t the most energy-efficient way to do things. So if you pay close attention (and watch the video), you’ll see two blued titanium carriages – one is part of the tourbillon and the other is connected to the wheel that winds the rementoire spring which is recharged every second. So one of the three-armed carriages moves around in one second increments around its own axis.

The escapement beats at 4 Hz on the T0

The escapement is fed via barrels simultaneously as opposed to in series. Though the power reserve is 72 hours and according to an article on the brand’s website, “a high accuracy was maintained for 50 hours out of 72 hours due to the constant-force.” The gear train uses components made from Seiko’s MEMS (Micro Electrical Mechanical System) technology. This was initially used on Seiko’s high-beat (5 Hz) movements; though more precise than slow-beating movements, there are few challenges associated with its development. For example, it consumes a lot more energy and the escapement wears out quickly due to increased friction.

Two barrels feed power to the gear train simultaneously

To solve this problem Seiko turned to MEMS technology hitherto used in the semiconductor fabrication. This process produces components that are lighter and more durable with a smoother surface. Though only the escape wheel and pallet fork were made using MEMS technology in the regular production models, the T10 has most of its gears made using this method.

The movement is based on the Caliber 9S65

Since the movement is based on the Caliber 9S65, the balance wheel oscillates at 4 Hz (28,800 vph), which may be the normal for modern mechanical watches, but not for those with a rementoire and tourbillon. The components of the movement are supposedly hand-finished to Grand Seiko’s exacting standards. Still in the concept stage, it may be a while longer before the T0 appears in a production timepiece, but those visiting the Grand Seiko Shizukuishi studio in Morioka (once the Covid-19 restrictions are lifted) can get a glimpse of this new movement.