Yes, this was the dilemma facing Amy Johnson/Jim Mollison, et al, with their compasses on the early trans-Atlantic flights. How many do you fit? So they fitted three, yet they were still paranoid things would go wrong and got spooked several times on the way! (By the way, I can't say I blame them!).Renegadenemo wrote:Ah, but if you only have two, how do you know which one is telling porkies? You need three so voting logic gets rid of the duffer. Even that doesn't work every time.
Our two systems operate by totally different methods, so the chances of them both being wrong simultaneously are millions to one against. The other thing in a WWSR scenario, of course, is that the driver will tend to have a pretty good idea of the speed he is going, just judging by the amount of throttle used over a particular timeframe of progressive acceleration and the distance travelled, so if a speedo suddenly shows 300 mph when a moment ago he knows he was doing 200 mph, he can be fairly confident it's the gauge that's wrong!