The abacus is an ancient calculating machine. This simple apparatus is thought to have originated in Babylon about 5,000 years ago. Today, the abacus is still used commonly in Japan, China, the Middle East, and Russia. In China, the abacus is called a suan pan, meaning "counting tray." In Japan, it is called a soroban. Japanese school children are still taught how to use the soroban, and competitions are held annually to find the most skillful calculators.

Historians think that the first abacus consisted of a shallow tray filled with fine sand or dust. Numbers were recorded and erased easily with a finger. The word abacus, in fact, may have come from the Semitic word for "dust," abq.

A modern abacus is made of wood or plastic. It consists of a rectangular frame about the size of a shoe-box lid. Within the frame are at least nine vertical rods strung with moveable beads. A horizontal crossbar...