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Buy, sell, or trade your watch here: http://www.thewatchbox.com Tim Mosso and Mike Michaels discuss the myth of the over-advanced perpetual calendar. Many watch collectors believe that if a perpetual calendar is set too far into the future, it must be sent back to the watch manufacturer's factory for correction. This state of affairs only applies to the IWC and Jaeger-LeCoultre watches that use IWC's "Kurt Klaus" perpetual calendar system. That system features a "year" indication, and all of the calendar elements (day, date, month, year, moonphase) are mechanically coordinated to move together in correct sequence. The drawback of this system is that it can be advanced too far into the future as the "year" window records a number years ahead of the present time. Because this calendar system only advances - it cannot be turned back - the owner must let the timepiece lie stationary until the displayed year and date is reached; alternatively, the watch can be returned to the factory for correction. Due to the year display, this perpetual calendar system also poses a hazard to buyers who may purchase a watch that has not run in years. For every year behind the current date, that unused watch must be indexed 365-366 times; the result can be a watch so far behind the current date that advancing it to the present would actually wear out the movement. In this instance, an IWC/JLC perpetual calendar might have to return to the factory because it fell TOO FAR BEHIND the current date. Finally, the vast majority of perpetual calendar systems do have the ability to be advanced through the four-year leap year cycle and back to the current day/date/month using pusher adjusters provided for corrections. While this may take some time (the leap year cycle covers 48 months), no intervention is necessary on the part of a watchmaker. Owners of perpetual calendars built by Ulysse Nardin and H. Moser & Cie have it even easier than this; these companies build perpetual calendar systems that can be driven forwards AND backwards, so an accidental overrun into the future takes only a moment's attention to correct. Due to the complexity of this system-dependent myth, Watchuwant rates it KINDA/SORTA true. Video and content by Tim Mosso and Pheline Jerome.