I might getting myself in a muddle. My Tom Tom must have really basic form of it then. When I go through a tunnel an I lose signal my TomTom must somehow know what speed I was doing when I lost signal in the tunnel and just carrys on moving the car assuming that I am doing the same speed through out the tunnel so it moves along whilst out of signal.
So I take it yours is just stuck on the screen or dash, and just has a wire down to the fag lighter socket?
Anyway, yup, my old mans TomTom does that too. But if he happens to slow down or stop, the TomTom still thinks he is moving forward, and when he eventually comes out the other side of the tunnel, the TomTom has way overshot. I never new SatNavs could suffer with premature ejaculation until I saw that.
And if you really wanna fcuk up a TomTom, do a U turn in a tunnel!
You actually really find out how good 'true' dead reckoning is in somewhere like London with big high rises, or when going thorough those mega long tunnels under the alps. Or even in the mountains on very close hairpin bends - many a time in Andorra I was amazed at how accurate the Audi OEM nav was - with roads literally overlapping or running parallel, and it always got the correct position. Oddly, when I was in Andorra, I didn't really see any dash mounted sat navs like TomToms.
