This mechanism displays the date, day, month and sometimes the moon phase and automatically adjusts the length of each month taking into account leap years.

Its mechanism considers that there is a leap year every four years, without taking into account that three secular years out of four are not leap years. Thus a calendar called perpetual calendar still has to be corrected three times every 400 years. The next four adjustments will be for the beginning of March of the years 2100, 2200, 2300 and 2500.

This mechanism invented in the 18th century often had at its beginning a display of 48 months on 360 degrees. It is only at the beginning of the 20th century that the display of the 12 months on 360 degrees appeared by integrating generally a complementary display of the current year.

There are also perpetual calendars with slow jump, semi-instantaneous jump and more rarely with instantaneous jump.