I don't know about the whole "accurate because of the autobahn" statement, that's like saying no one in the US is jobless because this is the land of opportunity. After all, a host of BMWs come from a plant in North Carolina, so I guess the autobahn theory goes out the window. Generally though, speedos are off by about 4-6%, so naturally, the difference between actual and indicated speed will increase as you go faster.