First revealed in 2016, the Double Balancier à Différential Constant is understood to be the sixth of Greubel Forsey’s eight horological innovations so far. It iterates and improves on the brand’s original double balance architecture of 2013. The Double Balancier à Différential Constant represents several novel ideas marshalled towards the goal of constant amplitude aiding superior chronometry. This piece is one of 33 produced as part of an ‘edition unique’.
The 43mm white gold case wears a polished, rounded bezel that meets a vertically satinated midcase while the display caseback has a rim that is brushed on top and polished in profile. The lugs, soldered on to the midcase, are straight with a gentle taper, and wear a polished finish. The rim around the display caseback wears the brand mark and words ‘Double Balancier’, its serial number out of 33 and precious metal hallmarks, all laser engraved. The watch comes on an alligator leather strap by Cousu Main and is secured by a substantial butterfly-style, spring loaded white gold clasp. It comes with an additional signed, white gold pin buckle.
The half dial, a visual hallmark of the brand, has a hemispherical quality to it. It wears a light grey frosted finish. It has a prominent printed Arabic 12 hour marker and batons from 11 till 3 o’clock. A printed chapter of minutes serves as a visual reference for the remainder of the dial. A black polished bridge lies on the edges of the dial, securing the going train of wheels as well as arrow-shaped, skeletonised hands. Seemingly worlds below the dial, on the baseplate, is the small but legible two-tone, sector-style seconds register.
The up/down-style indicator indexes reserve on a 72-hour scale from the stacked twin mainspring barrels that peek from underneath the half dial. As the name suggests, the watch features twin free sprung balances, inclined at 30º angles, their orientation and direction of spin direction opposing each other’s. The balances feature hairsprings with handmade overcoils and they manage an amplitude of 21,600 vibrations per hour. They are linked by a differential, framed by two H-shaped, mirror-polished bridges visible on both the dial and movement sides. This differential sits between the two balances.
While the angularity of the balances is a tool in the fight against positional errors, their oppositional spin is designed to cancel out each other’s error rate. The differential between them transmits a single rate – an average of the rate of both balances – thereby eliminating the already reduced margin of error of the beat rate by a further half.
Underneath the differential are twin spiral-shaped constant force springs. They are part of a constant force mechanism, storing four minutes’ worth of energy from the barrels, and releasing a steady amount at regular intervals, negating the effect of any drop off in energy stored in the mainspring. A four-minute timer sits atop the differential, while the wheels underlying the set up drive the hours and minutes hands.
In addition to the technical aspect, the watch is finely finished. The bridges anchoring the balances are rounded and mirror-polished, contrasting against the dark grey of the media-blasted baseplate. The wheels of the differential are framed by two bridges that are architectural in their form and drive home the depth of the movement. The aureate hue of the mainspring barrels, balances as well as the wheels of the going train and differential, add a warmth to an otherwise industrial aesthetic. The visible jewels are ensconced in gold chatons.
The movement side view is minimal, dominated by the media-blasted baseplate. The only visible component of the mechanics is the bridge anchoring the differential and the spiral-shaped spring of the constant force mechanism. The visible jewels in chaton add colour to the view. Two plaques, one bearing the brand name and the other the serial number out of 33, also adorn the baseplate.
The piece is a milestone piece in the history of one of the most technically proficient and innovative independent houses in watchmaking. It presents the full suite of its innovations towards forces that have traditionally impeded chronometry, in an exceedingly finely finished package.
If sold within the United Kingdom, this Greubel Forsey Double Balencier will be subject to 20% VAT
