This is a dynamic shared object (DSO) for PHP that will add calendar support. The calendar extension presents a series of functions to simplify converting between different calendar formats. The intermediary or standard it is based on is the Julian Day Count. The Julian Day Count is a count of days starting from January 1st, 4713 B.C. To convert between calendar systems, you must first convert to Julian Day Count, then to the calendar system of your choice. Julian Day Count is very different from the Julian Calendar! For more information on Julian Day Count, visit https://www.hermetic.ch/cal_stud/jdn.htm. For more information on calendar systems visit http://www.boogle.com/info/cal-overview.html. Excerpts from this page are included in these instructions, and are in quotes.