Unstructured Abacus

This week I thought that I'd go retro. Very, very retro. Long before computers and calculators, many people used abacuses (or abaci if you're fond of pretense) to perform complex calculations.

I've often played with abacuses (for some reason, a lot of dentists that I've gone to have had them in their waiting rooms) but I've never really understood how one is supposed to use them.

If, like me, you've been curious about this, the Abacus: The Art of Calculating Beads site will not only teach you how to use an abacus but it also provides an excellent history of the abacus as well as links to various abacus related sites, including a great Feynman anecdote and a truly nifty Java applet of an abacus.