Meanwhile, the secular calendar module is driven beginning with the 48-month wheel, which uses two fingers to actuate a year wheel with 50 teeth. The year wheel thus moves by two teeth every four years, completing one revolution per century.
The year cam then controls the travel of “A” in the illustration, a limiter beak that limits the sliding distance of the peripheral rotor to a value that corresponds to a 29-day month. When in an inactive position, the limiter beak retreats so as not to interfere with the sliding of the peripheral rotor. In the illustration, the beak is in an active position for a leap year; once it’s passed, it’ll move back down and remain inactive for the following three Februarys.