The best way of reading information from the orbital moon display is to imagine the balance wheel acting as the sun, shining towards the earth, partially lighting up the moon and our planet. Having more space in the movement to work with, the Terraluna is equipped with the most accurate moon phase indication that Lange ever created. It reproduces the synodic month of 29 days, 12 hours, 44 minutes, and 3 seconds so precisely that it takes 1058 years before the display needs to be corrected by one day. And although chances are that you will let the manual-wind movement wind down sometime much sooner than that, it still is a remarkable achievement.

As impressive as the aforementioned complication is, the in-house movement L096.1 goes way beyond that and offers a selection of true horological treats. Thanks to its twin-barrel  configuration it sports 14 days of power reserve – indicated by a disc, as seen at the 6 o’clock position on the face of the watch. To minimize the deterioration of chronometric performance as the movement is reaching the end of its power reserve, it is equipped with a constant force escapement. Its primary function is to provide extra torque, an extra “push” of energy, towards the escapement over the entire course of the power reserve. In the case of the Terraluna the remontoir – as the constant escapement is also referred to – releases an identical portion of the available energy to the balance in 10-second intervals, assuring that the torque remains constant. The result is a relatively stable amplitude and more consistent accuracy from the first day to the last.

Completing the list of features is the perpetual calendar. With four apertures on the dial – for the indication of the day of the week, month, leap years and the “outsize date” -, it packs one final, barely visible modification to make this not-so-ordinary complication just a bit more complex, and perhaps easier to use. Although not a completely unique feature by definition, it is something more rarely used owing to the difficulties linked its execution; the twist is that all displays of the calendar switch forward instantaneously at the end of the days and months. The main issue with this – especially with larger apertures – is to have sufficient power coming from the movement in order to enable the mechanisms to change not gradually, over the course of several minutes, but instantly, and simultaneously. According to Lange, to keep the power for the switching process as low as possible, the required energy is “gradually built up via a cam and then released abruptly at midnight”.

The instantaneous perpetual calendar, the extremely accurate moon phase display and the remontoir would all be very strong features for any and all manufactures. The Richard Lange “Terraluna” packs these under one roof – or dial, if you like – into a beast of a movement with 787 parts and a diameter of 37.3 millimeters. This necessitates the use of a rather large case – 45.5mm in diameter and 16.5 in height -, but that should be a justifiable sacrifice in terms of this array of truly special complications. Available in pink gold as reference 180.032, and in white gold as 180.026, the non-limited edition Richard Lange Perpetual Calendar “Terraluna” will retail for $216,400 and $215,100 respectively. alange-sohne.com