I have a g-tech pro, and I find it gives varied results. Things like a not completely smooth road, ever so slight turns, ultra noisy (unmuffled turbo rotary) can give really inaccurate readings. If u use it on a drag strip, it might be different, but if u just want to test a new mod you have done to your car, I wouldn't trust it. but considering my nearest drag strip is over 300klm away, I havent got much choice!! lets put it this way, dont take the figures that a g-tech spits out at you for gospel.