So, for instance, you wanted to know (as I sometimes do, for research) what day of the week, say December 3rd, 1942, fell on, you can simply look it up.
Or, for that matter, what day of the week your birthday will fall in in 23 years. You used to be able to buy perpetual calendars for the desk. Now they seem to be obsolete. I just thought it'd make a nifty free application.