The gauge measures pressure differential much like a vacuum gauge, much more sensitive than a vacuum gauge though. I plan on doing some testing with my Barracuda- yes I own one of those gauges, my understanding is to have the gauge in the cabin with windows/vents closed to isolate the gauge from turbulence. It wouldn't be difficult to have the reference in the engine compartment and the sense on the hood or in front of the grill, whatever you are looking to measure the difference of. The gauges pop up on E-bay, that's where I got mine. Oh ya, 0->1.0" hope that's enough range for what I want to do. If not I'll sell it and pick up another.