i practiced criminal defense law for some 28 years in Pittsburgh, PA and often did a lot of "speeding citation" cases. most citations state the driver was exceeding the speed limit by 10 miles per hour or more. on some occasions, usually in small towns, a driver would be charged with exceeding the posted speed limit by "5 mph." in those cases, i would often argue that the average auto manufacturer speedometer can vary 3-7 miles per hour over the actual speed of the vehicle and thus, a driver cited for driving "5 miles per hour" over the posted limit could not be found guilty if he testified that he was "going the posted speed limit" according to the speedometer in his car. in some cases, i brought in articles from various test facilities showing the OEM speedometer deviations. most judges would accept that defense. this "lawyer trick" was happening all over the State so the Pennsylvania Legislature added a statute to the motor vehicle code that provided that if a driver was charged with driving "5 miles per hour over the posted speed limit", a plea of guilty would not result in any points being assessed against the driver's license. in Pennsylvania, it is relatively easy to accumulate enough "points" to have your license suspended for a period of time. that statute ended the "factory speedometer" defense in a lot of my cases as after the statute was passed, i could usually get the policeman to just change the citation to "driving 5 miles per hour over posted speed limit" and the driver would plead guilty, pay the $300.00 fine and court costs and walk out of the courtroom. the drivers were happy, the State of Pennsylvania was happy collecting more fines, and i was happy because i walked out with a decent fee just for "negotiating the deal."