How do you know that the GPS speed is always 100% accurate?



I know that my T5's odometer is 5 km/h faster and I admit that I use the Navman's displayed speed as well, but after what once happened to me, I don't rely on it.
Anyway, while I was travelling at almost steady speed I've noticed that I've passed my turn and the GPS didn't say "turn left", so I'd quickly checked the GPS and surely it was frozen.

Just imagine that you trust it more than your car's odometer and got a massive fine for speeding, just because it's frozen or it lost a few satellites and the accuracy was out.

Oh, and my Amarok's speedo is almost 10km/h faster. I just don't see it as a big problem and am glad that VW designed it that way. Lesser chance to be booked for the speeding.