Did anyone read the link I posted. Its not the only link but pages after pages which I have read, all say that GPS is more accurate.
How accurate is your car speedometer? #AskTCE
What's more accurate: the car's speedo or the GPS? - The Globe and Mail
GPS speed vs Car Speedometer - GPS - Gadgets
How accurate is a GPS-based speedometer? | GPS Systems
Which Is More Accurate: Speedometer or GPS Device? - WSJ
How accurate is your speedo?