*You do need to be on a flat level surface
*You should have 300-lbs of ballast in the front seats so the car will have its 'driving' inclination
*Locate the spot where your diffuser will begin
*Measure its elevation above the ground
*Then measure back to where the diffuser will terminate to get your horizontal distance,your 'run.'
*If you have a scientific calculator,you can use the trigonometric function to get your dimension multiplier
*If say,you do use 4-degrees,enter: 4 tan,to get 0.069926.
*If you multiply your 'run' dimension by this value,it will give you your 'rise' at the back of the diffuser for 4-degrees.
*This will be the exact distance above your original starting elevation for the rear of the diffuser,to get your 4-degree slope.
