SIHH 2015: The Greubel Forsey QP à Equation with “Mechanical Computer”


Greubel Forsey QP a EquationWell-heeled collectors of ultra-complicated mechanical watches, and the haute retailers who supply them, should be in Seventh Heaven over Greubel Forsey’s seventh “Invention Piece,” the Greubel Forsey QP à Equation, unveiled to the watch intelligentsia today at SIHH 2015 in Geneva.

The Greubel Forsey QP à Equation is the first timepiece to incorporate into its movement an all-new mechanism that Greubel Forsey calls a “Computeur Mécanique,” or mechanical computer. This device, for which the brand has filed several patent applications, is a sub-assembly of 25 parts and partly inspired by the systems used in large astronomical clocks since the end of the 15th century, which managed the information that determined certain key dates in the ecclesiastical calendar in relation to astronomical data.

The mechanical “brain” at the center of this invention consists mainly of rotating, co-axial coded elements in an arrangement complemented by a system of programmed movable sections. Depending on its geometry and speed of rotation, each element generates its own indication in a cyclical, pre-programmed way. In this manner, the mechanical computer — which has been ingeniously miniaturized and integrated into the watch’s movement — is able to automatically display all the indications of the watch, each generated by its own co-axial coded element. In the case of the QP à Equation, these consist of all the functions of a perpetual calender, along with the equation of time: seasons, equinoxes, solstices, the equation of time, and the date, day, month and four-digit year. (One of the coded elements, for example, is specifically programmed to take into account and compensate for the differences of a leap year.)

Greubel Forsey QP a Equation - front
Greubel Forsey QP à Equation, front (above) and back (below)

Greubel Forsey QP a Equation - back

Despite the immense complexity of its mechanism, Greubel Forsey’s seventh invention is surprisingly simple to operate. All eight of the watch’s indications are controlled by a single selector set into the movement’s winding crown; the wearer can simply turn the crown in either direction to make adjustments without any risk of damage to the mechanism.

Greubel Forsey is a watch manufacturer that is not known for doing things simply — its first invention, after all, was an inclined double-tourbillon movement — and true to form, for the first application of its mechanical computer, it has chosen to focus on one of the rarest (and, frankly, probably least understood) astronomical complications, the Equation of Time — which is directly linked to the perpetual calendar.

Put simply, the equation of time measures the difference between “true” solar time and the more conventional “civil” or mean time, which is fixed at 24 hours per day, throughout the year. The length of a day in solar time varies according to the position of the earth on its elliptical orbit around the sun. For example, a solar day is about 16 minutes longer than a civil day in November, but about 14 minutes shorter in February. The unique display of the equation of time on the dial of the Greubel Forsey QP à Equation uses two sapphire crystal disks, driven by the mechanical computer, rotating independently to show the time difference as it changes throughout the year. The equinoxes and solstices, along with the four seasons, are also displayed in the equation of time indicator, located on the back side of the movement.

Greubel Forsey QP a Equation - dial CU
Close-up of the equation of time display
Greubel Forsey mechanical computer - sketch
Rendering of Greubel Forsey’s “Computeur Mécanique”
One Response to “SIHH 2015: The Greubel Forsey QP à Equation with “Mechanical Computer””

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  1. Some of the Greubel Forsey watches are a little too over the top when it comes to styling (for me) but I find this one really sticks a nice balance.

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