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Definition: abacus


One of the earliest counting instruments. Similar devices predate the Greek and Roman days. It uses sliding beads in columns that are divided in two by a center bar. The top is "heaven," where each of two beads is worth 5 when moved to the center bar. The bottom is "earth," where each of five beads is worth 1 when moved toward the center. See biquinary code.





An Abacus
The number appearing on this Chinese abacus is 1,532,786.