I checked my speedo out with a roadworks radar. The speed limit on the F3 was 80kph where they were working, and a big sign told you what you were doing as you approached. So I set my speedo to 90 kph to make sure I was over the limit, and the sign said I was doing 85.
Now I would like to know if the error is proportional, ie 42.5 when the speedo says 45, 113 when the speedo says 120, or else constant, ie 5 when I am standing still! I expect there is a mixture of zero-error and proportional error.
Zero error would be easy to fix, by shifting the needle on its shaft, but fixing proportional error would mean adjusting the tension in the needle return spring. Either way, it is a real hassle geting to the works of the instrument panel.
Mike