The same word which refers to a mathematial system developed independently by Isaac Newton and Gottfried Wilhelm Leibniz also refers to (1) a stone within the body, such as a stone in the urinary tract and (2) the calcium salt deposits on the teeth. These different meanings of calculus all go bach to the origin of the word. In Latin, a calculus is “a pebble.” Pebbles were once used for counting, from which came the mathematical field of calculus. A urinary calculus is literally a tiny pebble in the urinary system. And the calculus on the teeth is, therefore, a pebble in the teeth.