Isopsephy (IPA: [ˈaɪsəsɛfi], iso meaning "equal" and psephos meaning "pebble") is the Greek word for the practice of adding up the number values of the letters in a word to form a single number. The early Greeks used pebbles arranged in patterns to learn arithmetic and geometry. A Latin word for "pebbles" is "calculi", the origin of the word "calculate."