The new AVERAU 39 Moon phase collection is our modern reinterpretation of a classic watch complication.
One of the earliest known complications, the moon phase displays the sunlit portion of the moon, as observed from earth.
The moon completes its lunar cycle in 29 days, 12 hours, 44 minutes, and 2.8 seconds. Since the center wheel makes one rotation per hour, a series of gear ratios (forming a reducing gear train) can be used to transition from one hour to approximately one lunar cycle.
Our version is a modern reinterpretation of the classic Moon Phase complication: it shows both the Northern Hemisphere and the Southern Hemisphere views of the moon.