We brought early news of the announcement of the Greubel Forsey Différential d’Égalité just before SIHH, and here we present to you our hands-on review after spending some time with Stephen Forsey who explained the watch. We also handled it, examined it, and photographed it. Here is our review, with our analysis, high resolution photographs and technical notes.

All you need to know about the Greubel Forsey Différential d’Égalité

Make no mistake, this is a gorgeous looking watch. But like all Greubel Forsey watches, its a love it or hate it kind of timepiece. Its for those of us who marvel and are fascinated by the mechanics of timekeeping, and wonder at the 3 dimensional landscape (which led our Chief Editor to coin the term watchscapes). We are not be able to resist falling in love with these watches. Granted they are extremely expensive, but the conceptualization, the build quality is extremely high, and only the person putting up the money to buy such a piece can decide if its worth the admission price.

The Différential d’Égalité is no different from the other Greubel Forseys. The visual impact is powerful. Immediately captivating the eye as one gazes on the dial. Everything looks its part from the huge cut out which exposes the inclined balance to the hands and parts of the remontoire, to the frosted finish and the indices and the hands, to the colour scheme. All wow worthy.

The case, dial and hands

The case is the typical Greubel Forsey case. At 44mm in diamter and a height of 15.3mm, it has rather typical dimensions for GF as well, though one might note that the height is perhaps on the thinner side as GFs go. The lugs are highly curved, and as a result, the watch sits rather nicely on the wrist.

The dial layout is also classic Greubel Forsey. The dial itself is vestigial. The bulk of the surface on the dial side which is not part of the cutout is the back of the mainplate of the movement. The plates are maillechort, nickle-palladium plated and beautifully frosted. It also carries very beautifully done up bevelling, countersinks and anglage. What is left is an outer ring which is made in a multi-level synthetic sapphire glass. The hour ring with lacquered, and the hour markers are galvanic grown appliqués. The minute indices are engraved and laquered. The colour scheme of the lacquer is a mid-tone grey, and provides beautiful contrast to the frosted plate and the gold hue of the exposed wheel components.

A power reserve indicator pivots at 1 o’clock and shows the remaining time from 60 hours, where the watch is stopped by an internal mechanism to ensure isochrononicity to 0, in a fan shaped subdial. A small seconds hand is at the 4 o’clock position and carries the jumping seconds, and a separate, smaller continuously running seconds hand sits on a dial between the jumping seconds and the balance wheel.

The hour and minute hands are in gold with SuperLuminova.

The balance is inclined 30°, an angle which GF research shows as the most likely wrist angle in a wrist watch, and held in place by a magnificently polished bridge. Details on the finishing is found in our three part article where Stephen Forsey explains all of these. Part 1 is and Part 2 on Finishing, and Part 3 on the GF business, and Stephen’s personal heros.

The movement

The movement is where the action is, and GF has chosen to make it visible from the dial side. The nickle-palladium plated maillechort plate is further opened up to expose the barrel on the left to offer visual balance to the jumping seconds subdial on the right. The bottom lower left quarter is also cut open to expose the mechanism and the inclined balance with the magnificent bridge.

From the back, the movement features a circular plate with the signature Gruebel Forsey micro-writing, and an exposed section with highly polished levers being visible.

Movement finishing is top grade, and as good as it comes. This level of detailing and finishing is right at the top of the top of the haute horlogerie stakes, claiming true haute de gamme status. Every imaginable surface is detailed and treated in a superb fashion, leaving the parts which are shiny to gleam in delight, and the frosted or satinated or brushed parts to contrast beautifully. In terms of finissage, the Greubel Forsey Différential d’Égalité is beyond reproach. Ne plus ultra. Although we are not frequently given to colloquial expressions, the Chinese saying 没有马跑, especially effective when expressed in Hokkien as “bo beh chow”, comes to mind. Literally translated to “no horse run”, meaning that it stands peerless. Certainly an apt phrase, to describe the finishing on the Gruebel Forsey Différential d’Égalité, or indeed any Greubel Forsey.

Why constant force and the need for a remontoire

Remontoires were first developed for tower clocks. In order to provide for longer power reserves, most tower clocks have a reserve or 7 days and some even can go for a whole month between windings, the power source needs to be big. In a tower clock the power to the train is usually a weight which is hoisted up the tower and allowed to fall. As it descends, it supplies power to the train. Although this force remains fairly constant (after all gravity is a constant force), it is subject to imperfections in the gear train and variations in lubrication. Remember that in a huge clock from that era, operated on components which were large, heavy, and not finished. In order to smooth out these irregularities, a small spring is used to provide power to the train. This spring is placed within the wheel train, within the power flow. It is wound in fixed intervals by the falling weight. This spring is known as a remontoire.

In a spring driven clock or watch, the power source is the mainspring. This mainspring is by necessity is large, long and strong. As it unwinds, the torque follows Hooke’s Law, and depletes over time. When fully wound, the torque is very high, and when near depletion, the torque is much reduced. This variation in torque affects the escapement’s isochronism. Similarly, the remontoire is a small spring installed within the wheel train. By nature, this remontoire spring is small, it is able to supply a more constant torque to the train, but it also goes from full to depleted quickly, and needs to be rewound often. The mainspring’s power is used wind the remontoire. So that the movement can run for the full power reserve of the mainspring, while attaining the constant torque supplied by the smaller remontoire. Other solutions to this problem is provided by fusée and chain systems, and the ancient stackfreed.

Remontoires in wrist watches were first introduced by F.P. Journe in his Tourbillon Remontoir D’egalité in 1999. Journe fitted his tourbillon with a one second remontoire, which as the name implies discharges and rewinds once every second. This provides a near constant force to the tourbillon escapement. The system uses the remontoire to power a seconds morte (jumping seconds) mechanism. Journe followed up with his even more elegant Chronomètre Optimum. A similar technique is used in the Lange 31 and the Lange Zeitwerk. But the principal reason for the remontoire in the Langes is to ensure that the huge power of the mainspring, required because the Lange 31 has a power reserve of 31 days, and the Zeitwerk has to have sufficient power to ensure a clean jump of all 4 digits instantaneously. In SIHH 2017, Lange added the Richard Lange Jumping Seconds to her list of watches with remontoires, and utilize the staccatto effect of the rewind of the remontoire to power the seconds morte. A similar remontoire, executed differently is also used in the Jaeger LeCoultre Geomatic True Second.

There are remontoires and there are remontoires

A remontoire is defined (Daniels, Watchmaking) as a spring within the power train which acts as a secondary escapement for the mainspring. This spring rewinds at fixed intervals (1 second is a popular choice, but longer intervals exist, for example the Lange 31 features one which rewinds every 20s). And in so doing, feeding the balance with a smaller torque, and at a more constant rate than directly from the mainspring.

In the GF Différential d’Égalité, the constant force rewinding spring is in the power flow, being connected to the mainspring upstream and pari pasu with the standard (for GF) inclined balance via the spherical differential system. The jumping seconds is stopped and is reset when the crown is pulled out and the balance is also stopped to allow a precise time reset.

The constant force device the Gruebel Forsey Différential d’Égalité is thus more capable than the standard remontoire. In the GF system, Stephen Forsey explains that with the the spherical differential the energy to the escapement is even. The spherical differential is placed in the power flow after the third wheel, and it allows GF to split the power from the mainspring into two paths.

The first path goes to the remontoire spring, which is blocked but rewinds once a second. When the remontoire is blocked, the power to the balance spring comes from the remontoire spring directly. The remontoire unwinds during this stage, powering the escapement but only for one second before it unlocks and is recharged by the mainspring. This provides a more constant force to the balance than just the mainspring. As it rewinds, it moves one step forward, and as this occurs once a second, the output is used to move the jumping seconds hand. In a traditional remontoire, the balance does the unlocking. This has a destabilizing effect to the escapement, which is avoided here by using the differential to unlock the remontoire.

The other output path from the differential goes to the escapement therefore runs undisturbed as in the standard wheel train and displays the conventional seconds hand.

The competitive landscape

For the landscape, we limit to the watches which feature a remontoire mechanism with a non-tourbillon escapement. Of these there are not many. And of the few, none offer an inclined balance. None offer a differential system to split power either. The third characteristic is the zero reset mechanism which is built into the jumping seconds mechanism, and only one inhabitant in the landscape offers this feature to set the time precisely. Furthermore, at CHF 265,000 before taxes, the Greubel Forsey Différential d’Égalité is not a small chunk of change. No Greubel Forsey is and no matter how rich you are, this is a significant investment.

As mentioned, the earliest remontoire to be fitted in a wrist watch is on the F.P. Journe Souverain Tourbillon Remontoire d’Égalite (the link is to the latest iteration, although with a special black mother of pearl dial). The original Journe Series 1 (1999 to 2003) piece did not feature a jumping seconds, but showed the remontoire vane through an aperture on the dial. The Series 2 watches were then made with a rose gold movement (instead of rhodium plated brass in the Series 1) and feature a jumping seconds hand mounted on the remontoire). And the Journe Souverain does feature a tourbillon.

A. Lange & Söhne Richard Lange Jumping Seconds (€73,000 in pink gold and €78,000 in platinum with German VAT) is perhaps most similar to the Gruebel Forsey. It features a constant force mechanism via a remontoire and zero reset mechanism for the jumping seconds. The main jumping seconds hand takes pride of place as a very large regulator style subdial at 12 o’clock. However, as the remontoire is in line with the power flow of the movement train, there is no constant seconds hand. The Lange does not have a complicated differential system (the raison d’etre of the Greubel Forsey) nor does it need one, but gains points as it features a zero reset system. As is common with Lange, the finishing is also top drawer.

Perhaps we may also draw similarities to the Lange 1815 Homage to Walter Lange (€47,000 inclusive of German VAT ) as it is probably the only jumping seconds watch to feature both the seconds morte and a regular continuous second hands. Lange chose to do this particular watch sans remontoire, but by using a patent filed by F.A. Lange in 1867. This Lange has a special significance as a homage to the great great grandson of its founder, but also in his memory as Walter Lange passed away at the age of 93 on the second day of SIHH 2017.

F.P. Journe Chronomètre Optimum (S$125,200 in rose gold) is a possible candidate for the landscape. The movement is in the signature Journe rose gold, and it features two jumping seconds hand, one on the dial side, and the other which goes counter clockwise on the movement side, directly attached to the remontoire system. This Jorne a pure and elegant choice, being quite a bit smaller and slimmer, being offered in either a 40mm or 42mm case diameter with a height of only 10.1mm. In comparison, it does not have a zero reset, nor a differential system.

Grönefeld 1941 Remontoire (€44,990 before taxes for the steel version). This is perhaps a classical remontoire constant force system. The remontoire spring rewinds once every 8 seconds, hence no jumping seconds system is fitted. The movement is a speciality of the Gronefeld brothers, as it is made in stainless steel, and immaculately finished.

Further thoughts

What else can we say? We love the watch. It made our Chief Editor’s Top 5 from the 2018 Geneva Watch Shows list. And truth be told, we love the design aesthetic, the design, the technical virtuoso, and the finishing. But is the Gruebel Forsey Différential d’Égalité and its complicated spherical differential, its remontoire, its inclined balance a practical complication? Perhaps not, but then is any mechanical wrist watch practical in day to day use? It is but a reminder of the magnificence that man can achieve when he puts his mind to it, and the technical genius that goes behind the design, the thinking and the inventions that make the wristwatch the objet of our desires. And desire it we must.

Specifications and other details, including pricing is found in our original Press Release article.

Edited on 23 Feb, 2018 for added clarity in the functioning of the spherical differential and the remontoire.