Its a useful tool that if you know how to use it, it works pretty good and has done so on all my old race cars and others that I knew of actually. All you need know is the weight of your car and start with say a street car time slip. From there you can work out your current hp from weight/mph and then your new gearing/tyre size/actual on track hp/rpm needed to run whatever better number you want, which again if you know your stuff will dictate the parts you buy, takes a lot of the guessing out of it, but we are talking about cars that hook of course. Once up and running and you have your new quicker slip it can assist with showing you if your 60's are crap or not etc. etc.
