Each step in the algorithm simply subtracts the smaller number from the larger. This is done recursively by calling either gcd(m,n m) or gcd(m n,n): For example, the call gcd(494,130) makes the recursive call gcd(364,130), which makes the recursive call gcd(234,130), which makes the recursive call gcd(104,130), which makes the recursive call gcd(104,26), which makes the recursive call gcd(78,26), which makes the recursive call gcd(52,26), which makes the recursive call gcd(26,26), which returns 26. The value 26 is then successively returned all the way back up the chain to the original call gcd(494,130), which returns it to its caller.