From regulation No. 39, Type test approval of the Speedometer.
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