Mileometer and speedometer are not necesarily both overreading.
The older 'mechanical' head units had different internal drive mechanisms with the mileometer mechanically driven by gears (no reason for inaccurate measurement), where the speed reading was done magnetically, and is adjustable. The speedo on RTA reads slow (yes, I know, illegal, but I suspect it's a function of age - I feel slower nowadays too
), but the mileometer is reasonably accurate.
I know the electronic mileometers are also separate from the speed reading - the trip meter on my +4 did not agree with the main mileometer :shocked:. The only way to check is against measured road distances and these can be wildly inaccurate too
.
Cheers,
