The perpetual calendar mechanism (including a 12-month cam and a satellite cam for the month of February) is designed as a separate module with its own plate. This is a preferred solution for this movement, thanks to which the overall height of the caliber is smaller than with a partially integrated mechanism. The connection of the calendar with the basic movement is established with an intermediate wheel that engages with the hour-wheel pipe (a pinion that controls the minute hand). This second minute wheel is suspended between two jewels and meshes with a 24-hour wheel, also between jewels, which guarantees optimized energetic efficiency.
But the most innovative aspect is the single-line calendar display with four rotating disks, assuring optimized legibility, minimal energy consumption, and superb reliability. This mechanism alone required 118 additional parts in comparison with a conventional perpetual calendar display, including several bridges and wheels with jewel bearings that reduce energy consumption, especially of the two date disks. To keep all the indications on one plane without any overlap, Patek Philippe’s engineers developed a display system composed of two coplanar double ball bearings for which a patent application has been filed. The dependable date display and the perfect synchrony of the two date disks are optimized with an “anti-double-jump” feature for the units disk to prevent disk bounce in the event of a jolt or when a date correction is being performed (second patent application). The transition from the 31st day to the 1st day of the next month is the subject of the third patent application for a mechanism that immobilizes the units disk. This is done with a 31-point date star from which two teeth were removed.
The switching of the calendar displays is gradual. The display of the day, date, and month on a single line is complemented with two small round apertures, one at 4 o'clock for the leap year cycle and one at 8 o'clock for the day/night indicator. This information is very useful when the calendar needs to be set. The moon phases, an essential element of Patek Philippe’s perpetual calendars, are tracked with very high precision in a window within the subsidiary seconds dial at 6 o'clock. To facilitate the adjustment of the functions, three correctors – for the day, the date, and the month – are recessed in the case flank between 9 and 2 o’clock, in the same order as the respective displays. The moon phase corrector is positioned at 8 o'clock.
