While best known for its multi-axis and inclined tourbillons, Greubel Forsey has long experimented with other segments of the transmission inside a mechanical movement, aimed at solving some of watchmaking’s most basic problems; the Double Balancier à Différentiel Constant being a good example.

Almost a decade ago Greubel Forsey finished its différentiel d’égalité, a constant force mechanism that relies on a differential, which it incorporated into several models. Now at SIHH 2018, the watchmaker introduces one that gives pride of place to the invention, while adding, for the first time ever, a deadbeat seconds complication.

While it is nominally a time-only watch with a power reserve indicator – and an inclined balance wheel – the Différentiel d’Egalité wristwatch is named after the spherical differential with conical gearing, which receives energy from the mainspring barrel and releases it in constant amounts to the regulator through the course of its 60-hour power reserve.

In other words, the energy provided by the twin mainsprings doesn’t go straight to the escapement from the gear train, but instead winds a spring remontoir that in turn releases energy to the inclined escapement; the remontoir winds and discharges once a second.

And the second complication is one that’s often associated with the constant force mechanism, particularly those that work once a second like this one. The watch displays the deadbeat seconds at four o’clock on a large sub-dial and a conventional small seconds in smaller, lacquered sub dial just below.

Visible on the caseback is the black polished stop-seconds mechanism, as well as concentric laser relief engraved inscriptions in tiny script that explain the watchmaking values of Messrs Greubel and Forsey.

Measuring 44mm in diameter, the Différentiel d’Égalité is a white gold and is limited to 33 pieces.

Price and Availability

The Greubel Forsey Différentiel d’Égalité is priced at SFr265,000.