Euclid's algorithm is a method for finding the greatest common divisor (GCD) of two positive integers. It states that, for any two positive integers big and small such that big >= small (if big isn't >= small, then swap them). The GCD can be calculated as follows: 1. divide big by small to get the "remainder" (remember that big must be >= small and that remainder comes from MODULUS) 2. if the remainder is zero, then the GCD = small 3. otherwise set big equal to small and set small equal to the remainder 4. repeat steps 1, 2, and 3 until the remainder is zero