Abacus
Definition: An abacus is an ancient kind of calculating machine that keeps track of numbers by moving beads in grooves or along bars.
Other Definition: An abacus (plurals abacuses or abaci), also called a counting frame, is a calculating tool for performing arithmetical processes, often constructed as a wooden frame with beads sliding on wires. The user, called an abacist, slides counters by hand on rods or in grooves.
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