Rene,
mine under reads so 70 is 77 mph. That I understand is illegal. I believe car speedo should show the speed with a range of -0 to +10%.
Correct.
Both my 4/4 have under read speed (it's why I have added GPS based speedometers). I think in both cases (they were/are mechanical) that is likely due to lack of use by previous owners. However, as yours is electronic, it sounds as though it has been incorrectly calibrated.
