ETYM Latin abacus, abax, Greek abax.
(Irregular plural: abacuses).
1. A tablet placed horizontally on top of the capital of a column as an aid in supporting the architrave.
2. A tool used to perform arithmetic functions by manually sliding counters on rods or in grooves.
Frame with beads for calculation; Architecture, flat slab forming uppermost part of capital of column.
Ancient calculating device made up of a frame of parallel wires on which beads are strung. The method of calculating with a handful of stones on a “flat surface” (Latin abacus) was familiar to the Greeks and Romans, and used by earlier peoples, possibly even in ancient Babylon; it survives in the more sophisticated bead-frame form of the Russian schoty and the Japanese soroban. The abacus has been superseded by the electronic calculator.
The wires of a bead-frame abacus define place value (for example, in the decimal number system each successive wire, counting from right to left, would stand for ones, tens, hundreds, thousands, and so on) and beads are slid to the top of each wire in order to represent the digits of a particular number. On a simple decimal abacus, for example, the number 8,493 would be entered by sliding three beads on the first wire (three ones), nine beads on the second wire (nine tens), four beads on the third wire (four hundreds), and eight beads on the fourth wire (eight thousands).