Rene,
mine under reads so 70 is 77 mph. That I understand is illegal. I beleive car speedo should show the speed with a range of -0 to +10%.
The way my car is set up is n opportunity to lose my license.
Oh, John, yes. I was wrong. My speedo is optimistic and give me the illusion of a 120miles +4...
A speedo with showing you ´re to slow is also not roadlegal in Germany. And as Heinz sayed, if it shows you are too fast/ slow it´s the same difference in the distance you drive.
René