The Richard Lange Perpetual Calendar Terraluna was A. Lange & Söhne’s standout new release of SIHH in 2014. It is a superbly complicated timepiece with an instantaneous perpetual calendar and impressive 14 days of power reserve using Lange’s patented, constant force mechanism.

Flip the watch over, three concentric rotating disks made of solid gold poetically represent the earth, moon, and sky’s changing positions. The balance wheel at 5 o’clock represents the sun, and the earth disk completes a 360° rotation once per day, continuously indicating day, night, the current moon phase and the positions of the moon and sun as an observer in the northern hemisphere would see them. Accurate to one day over 1058 years, the outer sky and moon phase disks complete a rotation once per lunar month. When the moon disk is at 5 o’clock, between the sun (balance wheel) and earth disk, it appears dark blue to represent a new moon. The moon disk expands until the disk’s gold portion is fully exposed 14.77 days later upon reaching the 11 o’clock position – an innovative, first of its kind mechanism.

The perpetual calendar’s date indication is seen through the Lange’s signature oversized date apertures at 12 o’clock, and the month and day in smaller apertures separated at 4 and 8 o’clock respectively, with a small circular aperture for the leap year indicator at 2 o’clock. The power reserve indication is seen through a discreet aperture found at 6 o’clock.

Recently serviced by Lange, the present Richard Lange Perpetual Calendar Terraluna is hardly worn, and offered complete with its full set of accessories.