Why measure aero pressures:
Using a Magnehelic gauge to measure aero pressures (no more guessing or just using rules of thumb!):
Measuring surface body pressures:
..allowing you to do things like this:
Note the relatively high base (wake) pressure on the Jaguar, and how you can measure underside pressures as well. My measured on-road data (shown here) matched Jaguar's official data very well. Add the force vector for the panel angle and you can see which panels are causing drag and which are causing thrust.