Dont drive and record at the same time. I will try to do another test with a different vehicle so I have some sort of base on the mph. I still think this is a good gps especially for what I paid which is about $60. The garmin is the most used GPS out there but if your lucky you could find a used one for just under $100 but I've also seen that those can also be off by one or two mph. Either way hope this helps you out.
