What is a universal calendar?

It can be found in any Almanac. There is a calendar for every year, but there cannot be more than 14 different calendars - they merely repeat over and over. A universal calendar is keyed by numbers, with every year that matches that number. For example, you look up the calendar for 1973. It tells you it was calendar number "2" or which was the same calendar as 2001 and 2007. I collect calendars, and I have on the wall of my office right now, a drugstore calendar from 1956. It is the same dates for each month and day as 2012.