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A Lange & Söhne's perpetual calendars have been marking leap years since the late 19th century

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Lange 1 Tourbillon Perpetual Calendar.

Little leaplings born yesterday will have to wait four years to blow out birthday candles on the exact date.

Likewise perpetual calendars will once again switch from Feb 28 to 29, and subsequently jump to March 1 at midnight of the leap day in 2028.

In the meanwhile, A Lange & Söhne celebrates the intercalary day by placing nine models equipped with the perpetual calendar in the spotlight.

The complication, devised by English horologist Thomas Mudge, dates back to the mid-1700s. Technically, it emulates the durations of each month in the course of a year and is smart enough to identify a leap year.

Along with a peripheral month display, the Lange 1 Tourbillon Perpetual Calendar boasts an ingenious mechanism developed by the Glashütte-based brand.

A Lange & Söhne was born in this Saxon village in 1845. Founder Ferdinand Adolph Lange trained his first apprentices to become watchmakers and set up a new industry that restored the economy, which previously depended on silver mining in the Ore Mountains.

Leap year indication and peripheral month ring.

The earliest Lange pocket watches featuring a perpetual calendar as well as a moon-phase display appeared in the late 19th century.

Expropriated after World War II, the German company almost vanished in the latter half of the 20th century.

Following the fall of the Berlin Wall, fourth-generation Walter Lange revived its haute horlogerie in the early 1990s and introduced the first watches of the new era in 1994.

The inaugural foursome included the Lange 1 characterised by an off-centre dial and a novel outsize date, inspired by the five-minute clock in Dresden's Semper Opera House.

The date is indicated in a gold frame with numerals that are about three times larger than those in watches of comparable dimensions.

1815 Rattrapante Perpetual Calendar.

The patented outsize date was firstly combined with the calendar function in the Langematik Perpetual launched in 2001.

For this self-winding timepiece, the complication is driven by a traditional mechanism that maps the different durations of 48 months.

Corresponding to the four-year cycle, a programme wheel comprises 48 notches and steps. The deepest notches represent the four Februaries and the slightly shallower one marks the February with an additional day in a leap year.

The same system works its magic in six other models -- Datograph Perpetual; Datograph Perpetual Tourbillon; 1815 Rattrapante Perpetual Calendar; Richard Lange Perpetual Calendar Terraluna; Tourbograph Perpetual Pour Le Mérite; and Grand Complication.

In 2012, which happened to be a leap year, A Lange & Söhne took the complication to the next level for its Lange 1 Tourbillon Perpetual Calendar.

The unusual configuration of the dial poses a challenge in integrating multiple indications without affecting the asymmetric arrangement of the non-overlapping displays.

The solution is a patented peripheral ring that replaces a sub-dial to indicate the 12 months.

A tremendous amount of energy, however, is required to simultaneously switch all calendar displays particularly the peripheral month ring.

Lubricating the bearing of the programme wheel.

In-house calibre designers needed to find a way to innovatively sample the duration of each month and advance this ring by a large progression. In addition, it has to turn instantaneously by 30 degrees while switching to the new month.

The increment is about four times longer than that of the very lightweight and smaller programme wheel.

Driven by its internal gearing, the peripheral month ring rotates around its own axis once a year.

The inside of the gear rim is designed with a circumferential contour and wavy recesses. A spring-loaded sampler lever glides along this contour and "reads" the depth of the respective recess.

The more it is deflected, the shorter the month. In February, an extender of the sampler lever hits a cam beneath the leap-year disc. This makes the mechanism differentiate whether it is a common year with 28 days or a leap year with an extra day in February.

The sophisticated operation controls the outsize date, day of the week, month, leap year, moon phase and day/night indicators neatly arranged on the dial of the Lange 1 Tourbillon Perpetual Calendar.

Released in 2021, the Lange 1 Perpetual Calendar also functions via this inventive system, which like the conventional mechanism, recognises the different lengths of the months for an entire century.

Hence a correction is only necessary in the secular years 2100, 2200 and 2300, which according to the Gregorian calendar will not be leap years.

Datograph Perpetual Tourbillon.

Datograph Perpetual.

Lange 1 Perpetual Calendar.

Tourbograph Perpetual Pour Le Mérite.

Langematik Perpetual.

Richard Lange Perpetual Calendar Terraluna.

Grand Complication.

Lange 1 Tourbillon Perpetual Calendar.

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