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Accurate around the clock The perpetual calendar of the LANGE 1 TOURBILLON PERPETUAL CALENDAR

The development of a perpetual calendar for the LANGE 1 challenged Lange’s engineers and watchmakers in many respects. To preserve the characteristic design with the asymmetric arrangement of the time indications, the calendar displays had to be repositioned. The result was a totally new display concept with a peripheral month ring as its most salient design element.

A totally new mechanism was needed to execute the switching process for which the month ring has to traverse a relatively long distance because of its unusual position on the periphery. Thus, contrary to conventional mechanisms, the durations of the months are not coded on a separate programme wheel: they are sampled directly at the month ring. It features a contour with twelve recesses on its bottom side. A lever glides along this contour and “reads” the depths of the recesses. The deeper the recess, the shorter the month, and the earlier the switching process is triggered for the next month jump. In February, the extender of the sampler lever concurrently makes contact with a cam beneath the leap-year display. If it comes to rest against the larger radius of the cam, this means that the mechanism has to switch after 29 days (leap year). Otherwise, if it senses the smaller radius, the switching action in the month of February takes place after 28 days.

Sketch of a movement with a focus on the components of the perpetual calendar function

1 Month ring

2 Sampler leverExtender 

3 Extender

4 24-hour wheel

5 Leap-year display

6 Cam for the daily switching process

Ralph Knoll on the perpetual calendar mechanism

A watchmaker presents the LANGEMATIK PERPETUAL.

The force for the jump


A tremendous amount of energy is needed to simultaneously and instantaneously switch all calendar displays including the large month ring. This energy cannot be generated spontaneously – it has to be built up continuously. For this reason, Lange’s masters integrated two mechanical energy accumulators into the movement: one for switching the date, day of the week and moon phase on a daily basis, and the second one for switching the month ring. The energy for the daily switching process is built up via a 24-hour wheel driven by the motion work. Its arbor carries a cam whose increasing circumference is sampled by a spring-loaded lever. Every 24 hours, it drops off the apex of the cam, instantly pushing it – and the respective displays – forward by one increment. The energy accumulator for the monthly switching process is designed according to the same principle: a further cam is advanced incrementally every day by the programme wheel of the date display. At the end of a year, this not only causes the month ring to advance from December to January, but also moves the leap-year display forward by one increment. In this particular moment, all five displays advance instantaneously at the same time.

Exploded view of the calendar module, tourbillon, basic movement and rotor

1 Calendar module

2 Tourbillon

3 Basic movement

4 Rotor

The perpetual calendar mechanism

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