abacus
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[edit] noun
Ancient calculating device, usually made of beads on a stick or string.
A typical abacus would have several lines with 10 beads each, placed horizontally, one above the other. Each line would represent one digit, so that a bead on one line would be worth ten beads on the line below. Addition and subtraction is performed by sliding beads left and right. When all ten beads on one line are used, they are converted to one bead in the line above.
