That little device gets brought up a lot. I guess they are fairly accurate. I've never heard of anyone that brought one to the drag strip to compare times though. Most people use them to estimate 1/4 mile times. It does have a function that will calculate HP, but it has to be taken with a grain of salt. The only info. the G-tech has is the weight of your car (that you enter) and the time it took you to cover a given distance. That isn't a real reliable way to calculate HP if you ask me. hehe.