Hemisferium Perpetual CalendarThe Perpetual Calendar can find any date, day of the week and month from January 1, 1600 to December 31, 2799 including the bissextile years also known as leap years. The original piece on which this replica is designed was made in France between 1650 and 1700 and is kept at the National Maritime Museum in London. This vertical disc dial has two sides an altitude sundial and a perpetual calendar, which is the one depicted. The calendar consists of