The G-Tech Pro is a great tool & toy for automotive enthusiasts who want to test performance and verify modifications. They're quite accurate as long as you set them up properly (level them to 0.0 on the windshield & test on a level road). The only thing that comes into play that can affect readings slightly is the lift and dive of the nose of the car during acceleration & braking tests. I use one to "quick test" many things. But when it's time to get accurate, we break out the Competition Data Systems Commander II. G-Tech pro retails at $139.95, Comp Data TMII system $7,500. The G-Tech Pro is a great bang for the buck.
Happy Holidays,