As engine rpm increases, so does the amount of timing in degrees. This is how it is measured. On a motor with a supercharger, This device allows you to run a little more timing at lower rpm's w/o the threat of detonation in the upper rpm's. Example: if you have your BTM set at 1, than for every pound of boost the engine is under, the BTM retards or subtracts 1 degree of timing. So if at 6000 rpm's your total advanced timing was at 35 degrees, the BTM would pull the timing back to 25 degrees. Hope this helps out.