h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Its Zeller's congruence if I not much mistaken - I turned it into a neat program in Basic back in the 80's on a mainframe with teletype.

Forgot to say it was used to predict all the Friday 13ths using March 1st as start date which determines the whole year's Fri 13th then using March 1 to determine start day for year. I think that is right it is a long while ago.

Thanks GA,

Yes, it is known in mathematical circles as Zeller's Congruence. I wanted to avoid as much jargon as I could for this entry - to get non-mathematicians to try it. If you think it needs it, then I'll get the curators to add it in a footnote somewhere.

I used to write similar things on computers in the 1980s too, but I don't remember coming across this algorithm at the time. Our current computers/PDAs have a universal calendar programmed into them, so I'd guess they probably use Zeller's Congruence to do it.

Icy

I had a look at Zeller's entry on - hushed tones - Wiki. He was quite interesting so there may be some who would like to follow him up. Whether it needs a footnote, I'm not sure as those who know will not need it, but those who like the extra lead might well. It would do no harm to have it in.

My programing was part of my degree - BEd.