Just put a radar unit in the car and go---that's what I did.
Unless a speedo says right on it that it is "certified/calibrated" it aint. All cop cars have this printed on the speedo face so they can bone us speeders without the radar on. Phord allows up to 20% variation on their products, run into customers whining about it all the time. we all know ferrari speedos are generous, makes us feel warm and fuzzy inside thinking we are actually breaking the sound barrier.
