The book says to measure from seat to peddle then add 1 inch for the first slot then 1/2 in for next slot then 1/2 in for next slot. Each slot 1/2 inch lower than the other. Nothing about seat position. Keep your seat wherever its is now or most comfortable position for driving. So board neds to be at least 2inches longer than measurement. From seat to peddle. It does work nice.