Displayed behind glass, in perpetuity

Since making a comeback in October 1994, A. Lange Söhne has rekindled its watchmaking expertise at the manufacturer in Glashutte, Germany.

Tourbograph Perpetual Pour le Mérite.

Creating horological masterpieces is one of its aspirations, reflected in the Pour le Merite series, which debuted with a wristwatch featuring a tourbillion with a fusee-and-chain transmission.

Adding more complications throughout the years, the fifth combines the fusée-and-chain transmission with a tourbillion, a chronograph, a rattrapante function and a perpetual calendar.

The resulting 43mm Tourbograph Perpetual Pour le Mérite is a limited edition of 50 platinum-cased watches.

Horological challenges in creating the sophisticated model include orchestrating the interaction of the complex mechanisms in such a way as to prevent mechanical conflicts or unwanted energy loss.

In addition, the perpetual-calendar mechanism had to be built around the tourbillion, of which only about two-thirds of the movement surface was available.

A Lange Sohne

Of the 684 parts of the new movement, no fewer than 206 constitute the perpetual calendar with its analogue displays. While it will correctly indicate the duration of each month until 2100, a one-time correction will be needed on the last day of February of this secular year. From then on, the calendar will be correctly calibrated for the next century.

The three subsidiary dials show the date at 12 o’clock, the day at nine o’clock, and the month along with the leap year at three o’clock. The upper half of the analogue date also accommodates the moon-phase display, calculated to remain accurate for 122.6 years.

At six o’clock, the tourbillion spins while interacting with the fusée-and-chain transmission to offset two disruptive phenomena in a mechanical movement: gravity and waning spring force. Thus, they contribute to improved rate stability and accuracy.

A. Lange Söhne’s intelligent energy-management systems for mechanical movements include three different constant-force escapements as well as the fusée-and-chain transmission, the technical hallmark shared in Pour le Mérite timepieces.

In addition, the chronograph with rattrapante function features a fascinating split-seconds mechanism that can be observed through the sapphire-crystal caseback.

The combination of a perpetual calendar with a split-seconds chronograph is very rare, since power management must also be considered. In particular, the simultaneous use of several functions calls for mechanical ingenuity, for instance when the calendar indications advance around midnight and the stopwatch function is used at the same time.

Besides exceptional German engineering, the Tourbograph Perpetual appeals aesthetically, with a classic design inspired by A. Lange Söhne pocket watches, while the movement’s decorations and finish, as revealed through the sapphire-crystal caseback, showcase Saxon watchmaking artistry at its best.