Originally uploaded by mikeysklar
Those of you who know me already have learned what a fan I am of the doomsday in your head calendar trick. It is a simple method for calculating the day of the week for any day in any year. I've tried to explain it in person to most of my friends, but it is difficult to grasp that way. This site does a pretty good job teaching you how it works.
"It takes advantage of the fact that within any calendar year, the days of 4/4, 6/6, 8/8, 10/10, 12/12, and the last day of February always occur on the same day of the week—the so-called "doomsday" (and furthermore that other months have "doomsday" on the pairs 5/9 and 9/5 as well as 7/11 and 11/7..."