This is different in Germany but we learn about tolerance in driving school. Your speedometer can be wrong by about 10% and speed guns can also have errors. A good system accounts for unintentional speeding.
Displaying a speed slightly higher than actual speed is common and an acceptable margin of safety, such that if you are driving at the speed that the speedometer shows, you are more or less guaranteed to not exceed the speed limit.
This is different in Germany but we learn about tolerance in driving school. Your speedometer can be wrong by about 10% and speed guns can also have errors. A good system accounts for unintentional speeding.
Speedometers are not allowed to display a lower speed than the vehicle is running at all under EU regulation - see https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CELEX%3A42004X0331(01)&qid=1752829119241 § 5.3
Displaying a speed slightly higher than actual speed is common and an acceptable margin of safety, such that if you are driving at the speed that the speedometer shows, you are more or less guaranteed to not exceed the speed limit.