Moon-phase display A disc that rotates under the dial and is visible through an aperture. It shows the moon phases from full to new, generally as seen from the Northern Hemisphere.

Synodic lunation A synodic lunation of 29 days, 12 hours, 44 minutes, and 3 seconds is the average time between two full moons (or two new moons).

Connoisseurs of mechanical timepieces had to wait very long for two watches with | moon-phase displays that correctly depict the changing face of the Earth's companion as viewed from any latitude: The watches merely need to be switched at the equator crossing. The "Luna Mundi/Ursa Major" model in white gold shows the moon phases for the Northern Hemisphere while the "Luna Mundi/Southern Cross" in pink gold correctly reproduces them for the Southern Hemisphere. Both Lange moons emulate the cosmic original very realistically in two respects. On the one hand, they move continuously and not just in sudden increments once or twice a day as in conventional watches. On the other, the mechanism was computed so precisely that the displays deviate from the | synodic lunar orbit by only one day in 122.6 years. The calibre L901.8 movement in the "Luna Mundi/Ursa Major" has 398 individual parts. That of the "Luna Mundi/Southern Cross", the L901.7, requires four more parts, including an additional wheel that reverses the rotation of the moon disc. Both watches were available only in sets of two and the edition was limited to 101 sets. These timepieces were manufactured in 2003 and 2004.