The Tourbograph Perpetual “Pour le Mérite” is crafted in many meticulously executed steps.
Once the watchmaker has wrapped the delicate chain around the previously assembled mainspring barrel, they can integrate both components into the basic movement. The chain is then attached to the fusée. The planetary gearing or differential must be mounted first.
Using the ratchet wheel placed on the square barrel arbor, the watchmaker can adjust the final basic tension of the mainspring.
The tourbillon bridge firmly secures the cage to the chronograph bridge as it rotates suspended between two diamond endstones.
The chronograph and rattrapante mechanism is located on the movement side. It consists of a total of 136 parts. During the assembly phase, all of the individual parts of the elaborate column-wheel ensemble are manually tweaked and adjusted. This is because the wheels, levers, arbors and springs involved in the complex switching sequences must interact in a precisely defined order within fractions of a second to prevent mechanical conflicts.
The rattrapante hand arbor is about one centimetre long and extends from the dial to the rattrapante wheel on the opposite side of the movement. The arbor is turned from one piece of round hardened steel and painstakingly trued by hand. Then, it is passed through the hollow chronograph hand arbor.
Two column wheels control the chronograph functions. One of them deflects the arms of the rattrapante split-seconds clamp. The clamp is freely suspended so that its arms can centre themselves around the periphery of the rattrapante wheel, gripping it with uniform pressure from both sides. The surfaces of the clamp and the wheel are finished with straight and circular graining. The fine teeth of the wheel are roughened for a better grip.
The perpetual calendar correctly displays the different durations of the months in the 100-year cycle of the Gregorian calendar. The seven-stage transmission for the moon phases is calculated so precisely that it only needs a one-day correction after 122.6 years of uninterrupted operation. The deep blue hue of the white-gold lunar disc is the result of a patented coating process. Interference effects function like a filter that hides all non-blue colour spectra of the incident daylight. The crisply contoured stars are cut out of the coating with a laser beam.