Greubel Forsey opens new horizons with a revolutionary interpretation of one of the oldest watchmaking complications — the Perpetual Calendar. The inventive watchmakers in La Chaux-de-Fonds have also incorporated the Equation of Time in a demonstration of how to add complexity of function while simplifying with clear legibility and easy operation. Greubel Forsey has pushed beyond the previous limits of watchmaking, with no fewer than six major inventions, and a focus on ground-breaking inclined tourbillons. Now it’s time to reinvent the horological complication in the original sense of the term, and to show that in this area as well, watchmaking is in a perpetual state of evolution. The technically and ergonomically innovative Double Balancier 35° and GMT provided the springboard for this new take on the time-honoured perpetual calendar.

 The Mechanical Computer. The perpetual calendar remains one of the most representatives of horological complications and also one of the oldest. A direct descendant of the computus (Latin for calculation) that the clergy used to determine the religious and seasonal feasts of the seasons, these ancient mechanical perpetual calendars underpinned rural society from the early Middle Ages. A prime example can be found in the Strasbourg cathedral clock.

Comfort and clarity. This reinvention of the perpetual calendar integrates the Equation of Time into the perpetual calendar, as well as practical new functions and indications that improve clarity. The priority was to simplify the complete displays and make it easier to set the perpetual calendar by using the bi-directional winding crown. Despite the complete indications and functions, Greubel Forsey’s mechanical computer with Equation of Time is as easy to set as a simple date feature.

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, look at the back subdial for the displayed date’s Equation of Time.

By ©Greubel Forsey

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