Speedometer accuracy

[Quang]

is this 100% accurate? Mine seems to be 3-4mph off from my speedometer. Can anyone confirm this?

also i have a 2gb sd card, is there a more detailed version map of north american with more and accurate poi? And can I change the red arrow to a picture of a car or something on the ONE XL?

 

[Pedro2NR]

Hello and welcome.
Yes the GPS speed is more accurate than your car's speedometer.

You can not change the car icon with the ONE XL. This is only for the x20 range units.

 

[Locotuss]

I have confirmed the speed of the Tom Tom 510 with a Radar unit, mine has been 100 % accurate with the radar unit which is a certified unit.