Opus Perpetual – Erwin Sattler

This is how the perpetual calendar of caliber 2051 works: In the caliber 2051 from the manufacture Erwin Sattler, the centrally arranged hour wheel controls the calendar mechanism. As this rotates once around its own axis every 12 hours, the number of revolutions only needs to be halved once every 24 hours for the indications to advance correctly.

A so-called month cam is required to do justice to the special features of the Julian calendar with different lengths of month and a leap year after three normal years with 365 days. Raised and recessed areas provide the main gearshift, which scans the edge of this very specially shaped component, with information on the respective month length. Because February lasts three times 28 and then 29 days, a four-year wheel is also required, which rotates 90 degrees each year in a section of the month cam.

At the end of the month, the main shift lever interacts with a stepped worm disc. In months with 31 days, indicated by raised spots on the month cam, the beak of the main gearshift lever falls over the step as normal, thus advancing the date and month hands by one position.

However, if a month has fewer than 31 days, the rear end of the main shift lever plunges correspondingly deeper into the month cam. As a result, it extends further and the beak falls over the aforementioned step after 30, 29 or 28 days, thus causing the switch to advance to the first day of the following month. The day of the week and moon phase display remain unaffected. The calendar mechanism moves them forward by one position each day.