Perhaps not really an item for this post, but its the section of the site I use most often, so anyway: I've just bought a Navman 510. (Awesome by the way) When travelling at any speed, the Navman speed always shows 3 mph slower than the actual speed I am travelling, as indicated by my car's speedo. I recently noticed the same thing when travelling in a taxi. The guy had a Road Angel and this showed approx 6 mph slower than the car's speedo. I could understand a bit of intolerance when speeding up or slowing down because it must take a second or so for the GPS system to relay back to the satellite, but when travelling at a fixed speed, i.e. with cruise on, why is there a difference? Which is correct, car or Nav system? I would have thought that the car's speedo is more accurate only because of the distance the satellites are from the Navigation system, and I assume potential inaccuracies. /ubbthreads/images/graemlins/confused.gif Has anybody ever tried for instance measuring their cars speed against a radar gun or any other system for accuracy?? Just a topic for conversation, but would be interested for your thoughts.