The Pythagoreans-ancient Greek followers of the mathematician Pythagoras-were a brilliant lot.
They came up with the mathematical truism, The square of the length of the hypotenuse is equal to the sum of the squares of the lengths of the other two sides.
They also mathematically figured out the correct shape of Earth. In working out mathematical equations, the Pythagoreans practiced simplicity, using little rocks to represent numbers.
Thus, the word calculus means “pebbles” in Latin.