y set the calendar to be one of the following

   Gregorian   --- This is the calendar used daily the
                   Western Hemisphere. Leap years occur in this
                   calendar every 4 years except on centuries
                   such as 1900 that are not divisible by 400.

   Julian      --- This is the calendar that was in use prior
                   to October 15, 1582. Leap years occur every
                   4 years on the Julian Calendar (including all
                   centuries.)