It is a bit confusing at first, but i use it. First i hit the default button and it fills in a few things for me. So the desired octane stays blank. Desired ethanol is 30. Tank capacity I use 12.2 (I know its 12.4 but this way i can get exact mixes). %filled is how much fuel you have in your tank at the moment, I use the access port for the exact number. Octane rating is the octane of the gas (93 or 91). Ethanol octane rating is 115, and filled in with the default button. Gas % ethanol is 10 since regular fuel has some ethanol in it now. Try that out.