It uses the combination of the two relays being open or closed 00, 01, 10, 11, as a binary setup to select the speed. If I add a third relay, 000, 100, 010, 110, 001, 101, 011, 111, I get 8 speeds. I think I read it can do 16 speeds, but why??? I personally think 4 is good, 8 tops....