When introduced in 1994, the A. Lange & Söhne Tourbillon Pour le Mérite was the first wristwatch with a tourbillon and a fusée-and-chain transmission. Since then, every ‘Pour le Mérite’ watch has used this archaic energy transmission to power the watch. At SIHH 2017, the fifth watch with the appellation “Pour le Mérite” was introduced and it united five complications in a classically designed package.

Given the numerous complex mechanisms, the assembly of the 684-part manufacture caliber of the Tourbograph Perpetual ‘Pour le Mérite’ is a formidable challenge. Only the Maison’s best watchmakers work on the assembly of the movement. One of the biggest challenges for the watchmakers was keeping the thickness of the watch within reason.

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Just adding a perpetual calendar module to the 2005 model’s base caliber wouldn’t have cut it. So the team had to redesign the caliber with the perpetual calendar mechanism arranged under the dial around the tourbillon. “Even if each of the 684 parts is manufactured strictly within the micrometer tolerance range, the watchmaker still has to perform many minute adjustments to ensure that all the mechanisms work together perfectly as envisaged by the caliber engineers,” says Tony de Haas, director of product development.

We present seven images from seven important stages elaborate assembly process that will give you a sense of the complexity involved in the creation of this watch.

Assembly of the fusée-and-chain mechanism

This archaic power transmission method ensures steady torque

Once the watchmaker has wrapped the delicate chain around the 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. Inside the fusée, it ensures that the flow of power from the mainspring barrel to the escapement is not interrupted while the watch is being wound.

The ratchet wheel placed on the square barrel arbor

The 38-part mechanism handles this function in a space with a diameter of merely 8.6 mm. Using the ratchet wheel placed on the square barrel arbor, the watchmaker can adjust the final basic tension of the mainspring.

Assembly of the tourbillon

Before the filigreed tourbillon can be positioned in the basic movement, it will already have undergone a multitude of preparatory steps. It begins with the preliminary assembly of individual parts. Initial assembly is followed by adjustments, disassembly, final finissage and final assembly. The tourbillon bridge firmly secures the cage to the chronograph bridge as it rotates suspended between two diamond endstones.

The curved tourbillon bridge is immaculately black polished

The newly introduced curved shape of the tourbillon bridge posed new challenges to the finishing specialists. The black-polish technique applied to the surface of the steel part is finished to a mirror gloss so immaculately that incident light is reflected in only one direction. From all other perspectives, it appears to be jet black.

Assembly of the chronograph and rattrapante mechanism

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 column-wheel ensemble are manually tweaked and adjusted.

The chrono and rattrapante bits amount to 136 parts

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.

Assembly of the rattrapante wheel

The rattrapante hand arbor is about 1 cm 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 trued by hand. Then, it is passed through the hollow chronograph hand arbor.

The rattrapante wheel is dropped into the mix

Assembly of the rattrapante split-seconds clamp

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 the arms can center themselves around the periphery of the rattrapante wheel, gripping it with uniform pressure from both sides.

The arms of this clamp grip the rattrapante wheel

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.

Assembly of the perpetual calendar and the moonphase

The perpetual calendar mechanism arranged under the dial around the tourbillon in the interest of space and keeping the movement thin. 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 moonphase indication is accurate to 122.6 years

The deep blue hue of the white-gold lunar disc is the result of a patented coating process. The crisply contoured stars are cut out of the coating with a laser beam.

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