A perpetual calendar wristwatch is a type of watch that tracks and displays the date, day of the week, month, and leap years. The display usually features a moon phase indicator as well. What sets it apart from a regular calendar watch is its ability to automatically adjust for the varying lengths of months and leap years, without the need for manual adjustment. This means that the watch will accurately display the correct date even during leap years and won’t require adjustment until the year 2100, which is a non-leap year, considering that the watch will run continuously until then.