In the EU there is a law that says that a speedometer must always give a higher value than the real speed:
Quote:
5.3.
The speed indicated shall not be less than the true speed of the vehicle. At the test speeds specified in paragraph 5.2.5 above, there shall be the following relationship between the speed displayed (V1) and the true speed (V2).
0 ≤ (V1 – V2) ≤ 0,1 V2 + 4 km/h
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http://eur-lex.europa.eu/legal-conte...247290&from=EN