History is peppered with bad, sometimes horrible, sometimes despicable laws. Speeds limits, in theory, are not among them, however, in their enforcement a little tolerance in mechanical as well as human terms needs to be considered. For example, I don't believe citing for 1 MPH over a 35 MPH limit is adequate tolerance in either sense of the word. To me, 10% seems fair. (Not necessarily fun, but fair.)
Richard L.