Originally Posted by Guinness2702
Slightly more complicated than that
I use my satnav to calibrate it for real speeds.
Was true for my old ('93) Honda. Worked out as an increasing percentage from about 5-10% at low speeds to 10-15% at higher,motorway speeds.
But for my new (2005) Audi it's almost exactly 5mph above the satnav all through from 20 mph to Autobahn speeds!
So glad I don't have to do that bridge/tunnel any more, but thanks as it's useful info.