To explicate and clear what Kays has said, 100% is 1.00 and vise versa, and your creature's alignment does continuously fluctuate, except when it is 1.00 or -1.00, when, if it is 1.00, it can only fluctuate down but never up (in other words, your good is maxed out, so you can become more evil, but no more good), and it is just the opposite if you are -1.00.