IWC caliber 52850
Located at “12 o’clock” on the dial, IWC’s annual calendar shows the month, date and day in three separate windows. The mechanism automatically takes into account the differing lengths of individual months. Unlike a perpetual calendar, however, the annual calendar is unable to make allowance for the leap days in February or the leap years. Once a year, then, at the end of February, it requires manual correction. In the case of IWC’s annual calendar, the correction is made simply, via the crown.