Of the half-dozen commemorative editions Grand Seiko is rolling out to mark its 60th anniversary, one watch is significant over all the others, because it has a brand-new calibre that represents the first of a new generation of movements. A complete rethink of the 9S family of movements – first unveiled 22 years ago – the 9SA5 makes its debut in the Grand Seiko 60^th Anniversary Limited Edition (ref. SLGH002).

While the movement is cutting-edge for the brand, the design of the SLGH002 is a throwback to vintage Grand Seiko – the dial emulates the aesthetics of the first Grand Seiko 3180 of 1960 but with a modern twist, namely with widened hands and hour markers.

As a result, the dial is quintessential Grand Seiko, having a sculptural quality thanks to the broad dauphine hands and substantial, applied 18k gold hour markers. Even the frame around the date window is 18k gold.

The star above six o’clock indicates “SD”, or “special dial”, which means gold hour markers (and sometimes a gold dial)

Made of 18k yellow gold, the case has a diameter of 40 mm and a thickness of 11.7 mm. Most of its surfaces have a brushed finish, interspersed with wide, faceted bevels that are mirror polished.

The watch is notably thin for a self-winding Grand Seiko – the typical high-frequency Grand Seiko has a case just over 13 mm high – as a result of the new 9SA5 movement, which is the work of the Grand Seiko Studio Shizukuishi (formerly known as the Shizukuishi Watch Studio).

“A new chapter”

The crucial feature of the SLGH002 is the 9SA5, a movement that’s the first in a new family of 9S movements. Developed to “strike the perfect balance between precision, power and size”, the movement is a high-frequency, 5 Hz automatic with distinct features found for the first time in a Grand Seiko (or any Seiko, for that matter).

Most important is the new, patented escapement. Dubbed the Dual Impulse Escapement, it is Grand Seiko’s take on direct impulse escapement. Because it operates via a direct impulse to the balance wheel, generating minimal sliding friction (a characteristic of the traditional lever escapement), the new escapement functions with far greater efficiency.

While the Dual Impulse Escapement is reminiscent of George Daniel’s co-axial escapement – now widely used by Omega – Seiko’s escapement functions a little differently: the direct impulse occurs only in one direction of the balance wheel’s motion, and when the balance swings in the opposite direction, it transmit the impulse through the pallet fork like in a traditional escapement.

Furthermore, as in the latest, high-frequency Grand Seiko movement, the pallet fork and escapement are made using microelectromechanical systems (MEMS) technology – essentially a method of depositing tiny amounts of metal to build up a component – resulting in complex, skeletonised parts that are lighter and consequently operate with lower inertia.

The Dual Impulse Escapement

Also notable is the use of a overcoil balance spring – a first for a contemporary Grand Seiko (or any Seiko), which have always relied on flat hairsprings. The overcoil improves isochronism, which is the regularity of the balance wheel’s oscillation regardless of position or power reserve.

But it is not the more commonly-used Breguet overcoil. Instead, Seiko developed and optimised its own curve after running over 80,000 computer simulations to determine the ideal curve. But as with a traditional Breguet overcoil, the Seiko hairspring has to be curved by hand.

The free-sprung balance wheel with an overcoil hairspring

It doesn’t stop there: the 9SA5 also marks the introduction of the free-sprung balance wheel into Grand Seiko (and Seiko) movement. The balance wheel has has four adjustable poising screws recessed in the periphery of the balance wheel. And for maximum stability and shock resistance, the balance wheel is also supported on both sides by using a balance bridge, instead of the conventional balance cock that’s anchored only on one side.

Extra thin

Powering the 9SA5 are two barrels arranged in series – they unwind one after the other – both visible under the barrel bridge. As a result, the 9SA5 manages a power reserve of 80 hours, just over three days, while being 15% slimmer than the existing high-frequency 9S85 movement, which relies on a single, thicker mainspring. Another feature that contributes to the slimness is the redesigned, horizontal layout of the gear train.

The 9SA5 was also designed to incorporate subtle elements that are distinctly to Seiko: the curves of the bridges are inspired by the silhouette of Mount Iwate – the active volcano that overlooks the Grand Seiko Studio Shizukuishi – and also by a bend in the Shizukuishi River that runs near the workshop.

Despite all of the technical innovations in the 9SA5, Grand Seiko did not neglect the practical functions of the watch – the date display has been upgraded from the “dragging” date that slowly changes over at midnight, now standard for Grand Seiko movements, to an instantaneous date that jumps in the blink of an eye.

Key facts and price

Grand Seiko 60th Anniversary Limited Edition
Ref. SLGH002

Diameter: 40.0 mm
Height: 11.7 mm
Material: 18k yellow gold
Water resistance: 100 m

Movement: 9SA5
Features: Hours, minutes, seconds, and date
Winding: Automatic
Frequency: 36,000 beats per hour (5 Hz)
Power reserve: 80 hours

Strap: Crocodile with 18k yellow gold folding clasp

Limited edition: 100 watches
Availability: From August 2020 at Grand Seiko boutiques
Price: US$43,000, or ¥4.5 million (prices exclude tax)

For more, visit Seikowatches.com.