What feature distinguishes a perpetual calendar from a triple calendar?

A perpetual calendar is specifically designed to account for the varying lengths of months and leap years, allowing it to accurately keep track of the date indefinitely without requiring manual adjustments. This means that, unlike a triple calendar, which usually displays day, date, and month but may require setting adjustments at the end of each month or during leap years, a perpetual calendar will automatically adjust for these variations. Therefore, the distinguishing feature of a perpetual calendar is its capability to maintain accuracy without needing user intervention for adjustments.

This automatic adjustment capability is what sets it apart, making it a more sophisticated complication in watchmaking compared to triple calendars, which may not be able to manage such changes without user input.