Has nobody picked up yet that Clarkson made quite a silly point about the speedo/satnav screen.
He kept mentioning that although you knew where you were, you didn't know how fast you were going.
But if he had paid attention to the left screen, where he said "...which doesn't interest me at all..." then he would have noticed the speed at the centre bottom of the left screen.
Thus you do know how fast you are going, regardless of what the right screen is showing.
Quick snapshot of the bit where Clarkson just had the dragrace against James' 430, and says
"I have no idea how fast I'm going, but I'm know I'm somewhere near Guildford"