An abacus is a manual aid to calculating that consists of beads or disks that can be moved up and down on a series of sticks or strings within a usually wooden frame. The abacus itself doesn't calculate; it's simply a device for helping a human being to calculate by remembering what has been counted. The modern Chinese abacus, which is still widely used in China and other countries, dates from about 1200 A.D. It is possible that it derives from the earlier counting board s used around the Mediterranean as early as 300 B. C. An Aztec version of an abacus, circa 900-1000 A.D., is made from maize (corn) threaded through strings mounted in a wooden frame. There are Japanese and Russian versions of the abacus and several modern "improved" versions.
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