From Wikipedia ... "Calculate means to ascertain by computing. The English word derives from the Latin calculus, which originally meant a small stone in the gall bladder (from Latin calx). It also meant a pebble used for calculating, or a small stone used as a counter in an abacus (Latin abacus, Greek abax). The abacus was an instrument used by Greeks and Romans for arithmetic calculations, preceding the slide-rule and the electronic calculator, and consisted of perforated pebbles sliding on an iron bars."