I have several perpetual calendar pocket watches. I have some questions about these watches. I understand them to be watches that automatically adjust for the length of month and leap years. Is that correct? Are there different types of perpetual calendars? How complicated are the mechanisms needed to make perpetual calendars work? It seems to me that a perpetual calendar only makes sense if a watch runs continuously for years, which mechanical watches are unlikely to do for a variety of reasons, e.g., servicing. If so, do perpetual calendars ever make rationale sense?