A perpetual calendarPerpetual Calendar A perpetual calendar is a complication in a mechanical watch that automatically adjusts for the different lengths of the months, including February, and leap years, and (almost) never requires manual adjustments. It has a mechanism that takes into account the different number of days in each month, including leap years, and automatically adjusts the date, day, month and year accordingly [Learn More] is a complication in a mechanical watch that automatically adjusts for the different lengths of the months, including February, and leap years, and (almost) never requires manual adjustments. It has a mechanism that takes into account the different number of days in each month, including leap years, and automatically adjusts the date, day, month and year accordingly