RÉTROGRADE PERPÉTUEL

When you think of a grand complication, of course, it must include a perpetual calendar. Without exaggeration, guaranteed, it will be consulted every single time the watch is worn. Provided that one includes notions of “distinction” and “respect” under the umbrella of the term “useful”, a perpetual calendar is always one of the most useful complications in the watchmaking world.

Thus, it was a given from the outset that the Grande Double Sonnerie would be fitted with a perpetual calendar. However, the task would be far from easy. Even though Blancpain had a long-standing tradition of offering a wide range of ­ perpetual calendars in its collections, none of those constructions would be compatible with the design of the Grande Double Sonnerie. Blancpain’s existing perpetual constructions were all built upon a separate calendar plate placed above the regular running train of the watch. Surveying the landscape of perpetual calendars in the watch world, including, in particular, other grand complications, that method of construction has been employed almost without exception. However expedient and practical it may have been to follow the pack, that approach was ruled out. Placing a calendar plate above the rest of the movement would be completely inconsistent with the design imperative of offering a view of the exquisite complexity and fine finishes of the sonnerie from the dial side of the watch.

How then to create a perpetual mechanism that would fit on the dial side without a separate plate, without blocking the view of the sonnerie and without relegating the flying tourbillon to the back side of the timepiece? Not only did these conditions dictate that the calendar would have to be compact in its construction, its indications of date, day of the week, month and leap year also would have to be configured so as to permit an open movement aesthetic. And to add to the difficulty of what watchmakers term the “cahier des charges” (specifications), this meant that the perpetual mechanism would have to be fully integrated into the movement, a design challenge exceedingly rare in the universe of grand complications where layered plates are the general rule.

From a white sheet of paper, the design team developed an entirely new perpetual mechanism based upon a retrograde date display. Just as a perpetual calendar itself is a complication, incorporating a retrograde date should be seen as a complication of a complication. Not only must the mechanism keep track of the length of the months including leap years, it had to include a means to store energy so that the date display could smartly snap back to “1” at the end of each month. Further it had to offer protection against damage if time were adjusted backwards. One additional complication for Blancpain. Unique to all of its perpetual calendars and, for that matter, all of the Villeret complete calendars, setting of the indications is accomplished by means of correctors under the lugs which can be manipulated with a fingertip, obviating the need for both a tool and adjusting dimples on the flanks of the case. This patented design, unique to Blancpain, would have to be re-imagined to enable it to work with a compact retrograde design.

The solution positions the core elements of the perpetual calendar on the right side of the movement, leaving the view of the sonnerie on the left side largely unobstructed. The scale of retrograde date display is placed on the far left side (its serpentine hand pivoting from the center of the movement). For the day of the week and the combination month/leap year there are two separate subdials, both opened up to the maximum, with markings located on exterior rings.

In common with essentially all perpetual calendars, there are three hearts of the system. The first is a 24 hour wheel, the second is a program cam for the 12 months of the year; the third an additional cam element that turns once every four years for the leap year¹. Notwithstanding the presence of these “standard” elements, the design is 100 % new and unique to the Grande Double Sonnerie. The retrograde system brings the further complications of both a spring which is progressively armed with each daily change and a shock absorber to avoid both harshness in the return to zero and to prevent the return from going past “1”. The retrograde itself occurs rapidly, on the order of 20 milliseconds.

In common with all of Blancpain’s complicated calendars, the Grande Double Sonnerie’s perpetual mechanism incorporates security features to prevent damage if the owner attempts to set the calendar indications while an automatic daily change is in progress.

There was one further new design element confronted by Blancpain’s watchmakers: how to adapt the under lug corrector construction to this new movement configuration. Correctors for the other calendars found in the Villeret collection are placed under the lugs at the four corners of the movement². Connecting them to the mechanism is facilitated by a small arm that mates with a lever element of the calendar. With this architecture, there is a small spring which is fitted within the under lug corrector system itself. The spring serves to return the corrector back into position after every push. For the retrograde calendar, Blancpain had to redesign the system, relocating the springs into the movement itself.

Signaling the distinctiveness of each Grande Double Sonnerie, are the possibilities for customization of the calendar indications. The owner may choose the color for the calendar rings and the scale of the retrograde date as well as the language.

_{1 Blancpain’s other perpetual calendars program the leap years with a two-sided cam element that rotates every 8 years. Each of its two cams is active every four years. See Lettres du Brassus Issue No. 24.} 

_{2 Although every one of the complicated calendars places the correctors under the four lugs, for both the Equation du Temps Marchante and the Chinese Calendar, an additional corrector is placed at 9 o’clock.}