The abacus has been around for several thousand years, and it is an efficient and interesting counting machine. The standard abacus can be used to perform addition, subtraction, division, and multiplication, along with its use in extracting square roots and cubic roots. This site was created by Luis Fernandes, and it explores the wide world of the abacus through illustrations, thoughtful essays,...

Parents often scoff at the powerful calculators their children use for math classes, noting that they had to learn with slide rules. A device that predates both tools, however, is the focus of this unique site. The abacus has roots in the fifth century B.C., and still sees limited use in various parts of the world. A very thorough overview is provided online, with interactive applets that teach...