As it uses neither sub-dials nor apertures, this stunning timepiece turned the traditional perpetual calendar layout on its head and went for a central display of the calendar, yielding a unique three-dimensional aesthetic. Encircling the flying tourbillon, the day, month and date indications are, as a matter of fact, layers of movement bridges one atop the other. This is obviously no mean feat, as Cartier would have to redesign this movement from ground up in order for the bridges to function also as part of the dial. Reading it cannot be easier as three PVD-coated blue wheels trace their own individual courses with windows that single out the essential day, date and month. Leap year indication is found on the back.

Amazingly, this perpetual calendar movement, Calibre 9459 MC, uses no star wheels for the calendar mechanism save for one reserved solely for the day indication. According to Cartier’s head of fine watchmaking, Carole Forestier-Kasapi, this is because day and date can never be synchronised and thus need to be driven by separate mechanisms. In this movement, it is driven by a star wheel and can be manipulated by a secure corrector at two o’clock.

In addition, Calibre 9459 MC eschews the use of springs and levers, preferring to incorporate extra wheels because the latter yields higher chronometric stability. But that’s not all. Forestier-Kasapi revealed that the ‘secret weapon’ in this movement is what she terms ‘the brain’ – an intelligent system (patent pending) that replaces all the springs and levers. This mechanism consists of a wheel with 31 teeth, of which three are retractable. The wheel rotates once every 31 days and these teeth retract every end of the month. A two-cam system ‘informs’ the brain how many teeth to retract.

Says Forestier-Kasapi, “Normal perpetual calendars have very complex works with large yokes and are generally very susceptible to shock. We want to get rid of this problem. At the same time, the movement need lots of energy to advance the calendar so there are many ways to store energy for this purpose. Each time the date changes, there will be negative impact on chronometric stability. The change from February to March, especially on non-leap years, are the worst.”

By replacing spring-and-lever system with an innovative wheel driven system, the movement yields a whopping 80 per cent gain in chronometric stability. The entire movement consists of 382 parts, of which 67 are wheels. It is also more robust than ordinary perpetual calendars as, instead of correctors, the calendar is adjusted through the crown (with the exception of day of the week). Basically the possibility of over-winding or mishandling this perpetual calendar has been greatly reduced. More astoundingly, the Rotonde de Cartier AstroCalendaire bears the prestigious Poinçon de Genève and both its movement and case are individually numbered. With a 50-hour power reserve, this watch is limited to only 100 pieces in platinum and retails for around €150,000 (to be confirmed).