With the Equation du Temps complete calendar model, the Swiss Haute Horlogerie Manufacture Jaquet Droz presents a major accomplishment, a "Grande Complication" which sums up the stunning complexity of time... What is time? One cannot tame or capture it, and yet one lives by it alone. Second after second, it gives cadence to our lives. It measures each instant of our life. To attempt to grasp it, humankind had to observe the movement of the planets, to acquire the certainty that the earth's globe revolves around the sun. A duration was set for the earth's return to its point of departure: one year. This duration was then divided up and words were found to express the subdivisions: hours, minutes, seconds.
Above all, this rotation was thought to be "exact". But scholars quickly realised that it does not actually revolve in circles but pursues an irregular elliptical path around the sun. No day is exactly like another: this is no cliché, but corresponds to scientific reality: due to this irregular rotation, the duration of a day actually varies from 23 hours 44 minutes to 24 hours 14 minutes... This is real solar time. How could one live with this time? That is hard to say, since, for centuries, we have lived according to conventions that presuppose a perfectly circular rotation of the earth around the sun. We have fixed the subdivisions. Days become equal and of a conventional 24-hour duration. This is mean solar time, civil time, the time of our society and our time, which marks out our lives and runs regularly and precisely over watch dials.

With Equation du Temps, Jaquet Droz illustrates this difference between two times. Each February 12th, the solar time amounts to 14 minutes and 22 seconds more than civil time, and 16 minutes less each November 3rd. That is precisely the time indicated by the blued steel hand with "sun" tip in two shades of gold running over the slate-grey dial of the Equation du Temps watch by Jaquet Droz. Representing a supremely sophisticated touch, the hands that indicate the official conventions of mean solar time (hour, minute, date, month) are all of the "Lancine" type. Further enhancing this refinement, the two date and month subdials in the shape of opaline silver circles barely touching each other, are united by an applied metal ring, secured by blued-steel screws.
In tribute to the horological art exercised by the founder Pierre Jaquet Droz from 1738 in his first Manufacture in la Chaux-de-Fonds, the Jaquet Droz Calibre 3666-4 reveals its splendour through the sapphire crystal case-back. It is a mechanical self-winding, double barrel movement with 72-hour power-reserve, bridges, bars and plate adorned with "côtes de Genève" ribbing, secret signature, and a splendid 18-carat white gold oscillating weight with "sunray" decorative pattern. The Equation du Temps model with its 18-carat white gold case is crafted in a limited edition of 28, each individually numbered on the case-back.