# The Friday Fillip

Doomsday is coming. No, not Domesday of Book fame: that was 923 years ago, and has rather too much to do with law to be the subject of a fillip. I’m talking about February 28 or 29, depending, which is the day Rudy Limeback calls Doomsday for the purposes of his algorithm.

Now, I’m someone who had to use a calculator to figure out how many years ago 1028 was, so when I come upon something that begins “alg…” visions of my old math teacher, Amil H. J. Rintelman (I kid you not), appear before me and I quail. But you don’t have to be a savant to use Rudy’s Doomsday Algorithm. And why might you want to do that? Well, to know how to derive the day of the week for any date in the year — in your head.

Everything in the method is keyed to knowing the day of the week that the last day in February falls on. You then learn a formula for figuring out Doomsday for each other month. Once you know that all Doomsdays in 2009 are Saturdays, it’s easy to figure out what day of the week any given date is.

I’m not going to try to precis Rudy’s algorithm for you: he’s got it down to a science and I’d only muck it up. It doesn’t seem too hard to manage and it would be a neat parlour trick for the time your BlackBerry’s in your other coat or left on the bedside table.

Oh, and Rudy’s a Canuck, so he shows how to use the algorithm to figure out what date Thanksgiving falls on this, or any other, year. Bonus.