The perpetual calendar remains one of the most representative 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.
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.