arithmetic
Being good at mental arithmetic isn't going to gain you much street cred these days. But, as Owen Daniel explains, not so long ago it was a sure route to fame and fortune — even if you were a horse.
How to count without counting
John Napier was a clever man indeed. Besides inventing the logarithm, he developed ingenious calculating devices that fully exploit the power of the positional system. In this article Chris Sangwin tells you how to make your own set of Napier's bones and perform mathemagic with an interactive checker board.
