Greubel Forsey The invention that will make you an equation-of-time fan

— Greubel Forsey unveils its 7th invention, a wristworn calculator dubbed a “Computeur Mécanique” and capable of precisely indicating cyclical calendar phenomena. Its first application comes in the form of a QP à Equation (perpetual calendar with equation-of-time display) featuring unprecedented read-off simplicity.

Greubel Forsey, QP

While indubitably both a concept and a watch, this is anything but a concept watch! The 7th invention by Greubel Forsey is in fact a mechanical horological brain that is somewhat bizarrely presented in its French translation as a “Computeur Mécanique”.

While this invention is being introduced in a perpetual calendar model, the tandem from La Chaux-de-Fonds have warned that it might well appear in other creations from the Manufacture.

Taming cyclical phenomena

The primary vocation of this calculator/computer is to provide an accurate display of calendar indications, which are by nature highly variable. Topping the ranks of these indications that are a recurrent obsession among watchmakers are the equation of time, but also and above all leap years and their consequences. The latter notably include the necessity of ensuring that the extra day – February 29th – does not postpone the summer solstice to June 22nd! In a nutshell, this calculation module is capable of factoring in variables and indicating them in a simple way.

Greubel Forsey - QP

The dial side of the Greubel Forsey QP à Equation, providing no less than 11 indications while remaining perfectly legible
© Greubel Forsey

Legibility has indeed always been a concern among watchmakers. Many of them have ended up producing perpetual calendars with disastrously illegible, overly busy dials that have succumbed to the TMI (too much information) temptation. To solve this problem, Greubel Forsey has divided the data into two sets: conventional annual calendar indications appear the dial side; while the equation of time, seasons, solstices and equinoxes are shown on the caseback side.

A fleur-de-lis blossoms on the back

The back is indeed the place where the magic of this model truly weaves its spell. There is no trace of the usual hand showing the – 15 / + 15 equation-of-time indication. Although undoubtedly useful, this pointer serves only function: showing the positive or negative equation-of-time difference. This meant that in order to indicate all the other variables, such as the seasons, solstices and equinoxes, it would have had to be accompanied by a whole range of other apertures – and thereby fall into the trap of overloaded perpetual calendar dials.

Greubel Forsey - QP

Rear view of the Greubel Forsey QP à Equation, highlighting its large four-digit date display.
© Greubel Forsey

To avoid this, Greubel Forsey has come up with a clever device capable of indicating everything through a single, astonishing fleur-de-lis shape. The information is provided by two superimposed sapphire discs moving at different speeds. Checking the equation of time becomes child’s play, as it is read off at the exact spot where this fleur-de-lis intersects with a graduated vertical minutes scale. A red line along the flower means the difference is positive, whereas a blue line shows that it is negative. Meanwhile, the tip of the flower simply indicates the solstices or equinoxes along a circumferential scale displaying the four seasons in distinctive colours.

Like all great ideas, this fleur-de-lis looks like a self-evident read-off solution. All to the good, since that was the intention behind it. The casual observer remains blissfully ignorant of the intense thought process that preceded its development and it offers further eloquent proof of the impressive innovative capacity cultivated by Greubel Forsey, which has only just celebrated its 10th anniversary.

Greubel Forsey - QP

The fleur-de-lis on the caseback of the QP model, in this instance showing +8 minutes in relation to solar time on the date of the winter solstice: December 21st.
© Greubel Forsey

Exemplary dial readability        

On the dial side, Greubel Forsey has adopted the same attitude of optimising legibility and clarity. The complete calendar occupies most of the dial, showing the day and month along with an appreciably large date that is of obvious use in daily life, since this is the most frequently checked indication. It is indeed in this same spirit – based on the premise that even the most absent-minded owner at least is aware of the current year – that Greubel Forsey has transferred that particular indication to the caseback side, thereby simplifying the dial layout.

Among the other details that are typical signature features of the Manufacture, three in particular stand out. Firstly, a discreet window at 7 o’clock serves as a 24-hour display. Secondly, on the opposite side of the dial, a power-reserve sector at 3 o’clock comprises a red zone at the end showing the remaining time during which the isochronism of the model will no longer be guaranteed. Thirdly and finally, just below it, a discreet “QP/HM” signal indicates whether or not the single crown is activated, in order not to disturb the smooth running of the perpetual calendar when the watch merely needs adjusting by a few minutes.

Alongside this major invention, Greubel Forsey also introduced two variations of its GMT: one with a 5N pink gold movement, and the other in a black version.

Greubel Forsey - GMT 5N

The new GMT in a black-finish version.
© Greubel Forsey


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