Work out, in your head, the day of the week corresponding to any date — eg. today is 2009-11-22, a Sunday — using this method. (Wikipedia page, but I recommend the first link). If you stick to just years from 1900 onwards it’s very simple. Could be a geeky ice-breaker at parties to tell people what day they were born on.
I’m fairly certain I remember a TV one-off in the 1980s where some unfortunate autistic man was subjected to a “Mastermind“-style interrogation. The only thing this poor man could do was tell the day of the week for any date. Probably he’d stumbled upon this method …
Richard WM Jones 