A calculator that performs arithmetic functions by manually sliding counters on rods or in grooves WordNet 3.0 & Open English WordNet

The abacus, also called a counting frame, is a hand-operated calculating tool of unknown origin used since ancient times in the ancient Near East, Europe, China, and Russia, millennia before the adoption of the Hindu-Arabic numeral system. Wikipedia

A Greek and Latin board for calculating or playing. OmegaWiki

A device used for performing arithmetical calculations; (rare) a table on which loose counters are placed, or (more commonly) an instrument with beads sliding on rods, or counters in grooves, with one row of beads or counters representing units, the next tens, etc. Wiktionary

Device for performing arithmetical calculations. Wiktionary (translation)