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QP à Équation

20 May 2020

Following the GPHG (Grand Prix d’Horlogerie de Genève) award for the best Calendar Prize, Greubel Forsey presents its QP à Équation in a 5N red gold millesime with a chocolate coloured gold dial. By reinventing the prestigious perpetual Calendar (QP), with the QP à Équation, Greubel Forsey demonstrates through their art of invention that the history of mechanical watchmaking remains in a perpetual state of evolution.

Readability and displays

This reinvention of the perpetual calendar integrates the Equation of Time into the perpetual calendar, as well as bringing practical new functions and indications that improve clarity. The priority was to simplify a complete perpetual calendar display and yet make it much easier to set by simply using the bi- directional crown. Despite the numerous indications and functions, Greubel Forsey’s Mechanical Computer is as easy to set as a simple date feature.

To meet this technical challenge Greubel Forsey invented a sophisticated coding mechanism: the patented Mechanical Computer. A stack of cams with movable fingers shift the indications on the dial and caseback of the timepiece and the complete mechanism is fully integrated within the movement. The month’s cam changes the month, displayed in a window on the front and also moves the Equation of Time disc on the back. The years’ cam controls the leap year indication on the front and also the millesime and seasons on the back. The development of this coding device not only overturns the conventional way of setting the indications but also displays them simultaneously on both dial and caseback.

Just a glance at the calendar display clearly reveals

the three in-line windows that clearly indicate the day, the date and the month. The large date makes the calendar extremely legible.

Two sides showing 15 indications

The dial side of the QP à Équation indicates leap years, the 24 hours of the day and night, the day of the week, the large date, the month, the hours, the minutes and the seconds, as well as the 72-hour chronometric power reserve.

On the movement side, this timepiece displays the Equation of Time with the months, seasons, solstices and equinoxes, as well as the calendar year.

The Equation of Time

The Equation of Time merits further explanation. Horology seeks to measure time as regularly as possible; however the Earth orbits the Sun in an elliptical path. As the Earth sweeps close past the Sun, the period between successive solar zeniths, or the solar day’s length, changes. This causes the difference between solar time and mean time to vary from a few seconds to as much as 16 minutes during the year. The Equation of Time is the conversion factor between solar and mean time. To read solar time, simply look at the back subdial for the displayed date’s Equation of Time.

Greubel Forsey continues to put time to better service; where the caseback of the timepiece is not just there to showcase fine hand finishing, but also provides a new way to tell the time. The most frequently sought calendar information, namely the day, date and month, is displayed on the inline main dial display. Information that is less often required is visible on the back of the timepiece. Thus the two sides show indications that you need to know regularly on the front, and indications accessed less frequently on the back.

Chronometry with ease

The timekeeping performance comes from Greubel Forsey’s third invention: the Tourbillon 24 Secondes, with its unique fast rotational speed and inclined angle to solve the problem of critical positions of the oscillator in relation to gravity. A 25° angle and the rapid revolution of the tourbillon cage significantly improve the chronometric performance of a system containing only one tourbillon, especially in stable positions.

The multi-level chocolate-coloured gold dial of this millesime edition timepiece contrasts harmoniously with the 5N red gold case and underlines the intuitive linear calendar display. Herein lies the happy paradox: it is an ultra-complicated timepiece with complete perpetual calendar, tourbillon and Equation of Time function, however, it is just as easy to use and adjust as a three hands watch. Thanks to the bi-directional correction, it can be easily adjusted in both directions without risk of damage to the movement.