The undisputed star of A. Lange & Söhne’s 2014 collection, the Richard Lange Perpetual Calendar Terraluna is remarkable on many levels. Beginning with its most obvious characteristics, it is the first Richard Lange model to feature a the signature Lange outsized date. Like the Richard Lange Tourbillon “Pour Le Mérite” of 2011, it also adopts a regulator-style dial design. The inspiration for this comes from one Johann Heinrich Seyffert who made, in 1807, a world famous regulator which resides today in the Mathematics and Physics Salon in Dresden. Seyffert had been instrumental in transforming Dresden into a hub of precision horology in the early 19th century.

Lange has made several perpetual calendars till date and none of them follows the typical four-counter layout as the manufacture favours a pure aesthetic. This watch is no exception. The date is, very obviously, read through the two prominent apertures at 12 o’clock. Day of the week and month of the year are read off two smaller apertures within the small seconds circle and hour circle respectively. Leap year indication is displayed in red, next to the 15th minute numeral. All of its calendrical displays switch instantaneously, and this perpetual calendar remains accurate till the year 2100.

Boasting a 14-day long power reserve, this slender window at six o’clock clearly informs the wearer of the movement’s state of wind. To keep the power for the instantaneous switching process as low as possible, the required energy isn’t robbed from the going train, but rather, gradually built up via a cam over a period of one month and released in one swift motion at the stroke of midnight.

Calibre L096.1 is a double barrel manually-wound movement. To ensure that the 14 days of running power is delivered smoothly to the balance, the master watchmakers at A. Lange & Söhne incorporated a constant force escapement to regulate the power flow and keep the rate stable. In 10-second intervals, the constant force escapement releases an identical portion of energy to the balance, thus ensuring that torque remains constant, and that amplitude doesn’t vary. Therefore, high rate accuracy is assured from the first day to the last. In addition to the balance spring, the remontoir spring of the constant-force escapement is also made in-house .

Calibre L096.1, however, hides a secret – one that only the wearer and true Lange connoisseurs know. Revealed through the expansive case back, a unique orbital moon phase display shows not only the phases of the moon but also the location of the moon relative to the earth and the sun. This is a world’s first in a wristwatch.

The display consists of three discs. On the star-studded celestial disc, the moon – visible through a round aperture – orbits around the earth anti-clockwise once a month. The mechanism reproduces the synodic month of 29 days, 12 hours, 44 minutes, and 3 seconds so precisely that it takes 1,058 years before the display needs to be corrected by one day. Beneath it, the lunar disc rotates, featuring two round new moons. The progression of the moon phases can be observed through the aperture in the celestial disc.

In the constellation view, the position of the sun is occupied by the balance. On new-moon days, the dark moon stands between the earth and the sun. It appears as a bright sphere on the opposite side of the earth on full-moon days. Thus, the position and phase of the moon are indicated simultaneously. In the centre of the display, the earth rotates about its own axis once a day. It is daytime on the half that faces the sun (the balance) and night-time on the other. The peripheral 24-hour scale provides a time-of-day reference for the northern hemisphere.

Above: Position of the sun (represented by the balance) in relation to the moon and earth

Above: Gibbous moon

Above: New moon

Above: Full moon

Above: Gibbous moon

Under the dial, an intricate network of star wheels, springs, cams, yokes, racks and wheels – all beautifully finished and chamfered – affirms A. Lange & Söhne’s traditional values in watchmaking.

Above: Richard Lange Perpetual Calendar Terraluna in white gold, case diameter 45.5mm

Above: Richard Lange Perpetual Calendar Terraluna in pink gold, case diameter 45.5mm