I meant under read. As in display a speed lower than the one you're travelling at. Mathematically this is as near as impossible for me to not believe that there is a law against it.
Your quote also makes no mention of this being governed by law. In fact your quote implies that it is not governed by law, and the Police have to take into account that a percentage will under read
I asked one of our HMI team about this after reading this thread. It is against the law (legislation) for a speedometer to underread. I can probably chase them down for the appropriate spec but seemed like too much effort for this forum
Apparently, what is normally done with analogue instrumentation is it is designed to overread by a few percents with a tolerance of much less than that. So even something on the far end of the bell will still be over-reading, but by less than the mean. This satisfies the -0% to +10% tolerance that is permissable.
With electronics any sensor that is beyond tolerance will fail its end of line test (and believe me, they test
every unit... I have been to a Tier 1 factory where they are producing four million complex (electronics, buttons, and plastic encapsulation) components a year for one of the German OEMs, every single unit goes through an automated EoL test and has appropriate documentation produced to verify every step of manufacture including test. It's one of the more impressive things I've seen.). All of the needles in your car now are using stepper-motors anyway and they have a very tight tolerance in manufacture.
