By Kien Lee  | Photos: Lange 1 Perpetual Calendar in 950 Platinum

2024 welcomes an additional day in February as a leap year, with 29 February an opportune moment to admire once  the Perpetual Calendar of A. Lange & Söhne in its full glory.

A. Lange & Söhne has since 2001, launched nine timepieces boasting the Perpetual Calendar complication. What's unique about the Saxon manufacture's approach is its fundamentally different technical approach to the perpetual calendar mechanism, which have been deployed in the LANGE 1 TOURBILLON PERPETUAL CALENDAR and the LANGE 1 PERPETUAL CALENDAR.

Seven out of nine sophisticated A. Lange & Söhne timepieces with a perpetual calendar adopt the classical approach, which is defined by a programme wheel with 48 notches and steps, corresponding to the different durations of the 48 months in the four-year cycle of three regular years and a leap year.

While the wheel rotates only once every four years, the notches and steps are sampled by a lever. The rule is the deeper the notch, the sooner the mechanism switches to the first day of the next month. The deepest notches correspond to the four Februaries. One of these four notches is slightly shallower, demarcating the February of the leap year with an additional calendar day.

This mechanism recognises the different lengths of the months for an entire century, meaning a correction is only necessary in the secular years 2100, 2200 and 2300, which according to the Gregorian calendar will not be leap years.

In the fourth year of the leap year cycle, the indication switches to 4. The Perpetual Calendar takes into consideration that this year (2024) will welcome a 29th of February, and the complication works to ensure this date is displayed, making it the key difference with an Annual Calendar.

Meanwhile, the launch of the LANGE 1 TOURBILLON PERPETUAL CALENDAR in 2012 required the Manufacture to harmoniously integrate the multitude of calendar indications into the dial architecture of the LANGE 1 without affecting the asymmetric arrangement of non-overlapping displays - the dial of the LANGE 1 is notable, and iconic, for its off-centre dial configuration and the novel outsize date.

This new approach to the Perpetual Calendar complication is subsequently used in the LANGE 1 PERPETUAL CALENDAR which was introduced in 2021.

A. Lange & Söhne has managed a workaround, innovating with a patented peripheral month ring, which constituted an entirely new type of month display. It replaces the traditional mechanism in which the month is advanced by a notched programme wheel that the classical approach utilizes.

This new month ring is driven via its internal gearing, rotating around its own axis once a year. The inside of the gear rim features a circumferential contour with wavy recesses.

A spring-loaded sampler lever glides along this contour and is deflected by a magnitude that corresponds to the depth of the respective recess. The more it is deflected, the shorter the month.

In February, an extender of the sampler lever contacts a cam beneath the leap-year disc. This tells the mechanism whether it is a common year with only 28 days in February or a leap year with 29 days.

The commitment by, and motto of, A. Lange & Söhne to "Never Stand Still" is underscored by the manufacture's constant pursuit of refinement and innovation, and none more so objectified by its approach to the Perpetual Calendar complication. It is a philosophy that extends to its whole product roll-out, adding to its highly sought after status amongst watch collectors worldwide.