# Abacus

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.

On an abacus, the heaven beads have five times the value of the earth beads. (Reproduced by permission of
The Gale Group
.)

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 perpendicular to the rods separates the abacus into two unequal parts. The beads above the crossbar are known as heaven beads, and those below the crossbar are called earth beads.

To operate, an abacus is placed flat and all beads are pushed towards the outer edges, away from the crossbar. Beads are then slid upward or downward to represent a number. The number 7, for example, is represented by moving one heaven bead (worth 5) downward toward the crossbar and two earth beads (worth one each) upward toward the crossbar. The number 24 is represented by moving two earth beads on the second rod (worth 10 each) and four earth beads on the first rod (worth 1 each) upward. Addition, subtraction, and even lengthy multiplication and division problems can be solved with an abacus. Advanced users can even find the square root of any number.