May be quicker to visit the GoMoG workshop manual, (
www.gomog.com) look up instruments and gauges from the index, and then section 6 of that deals with speedos. There is a very good manufacturers manual included for modern electronic instruments where you will find a simple way to nudge it up or down, though they recommend its done on a rolling road. (that may only be for safety or maybe because you would have something to calibrate against, but as we know, a gps is fine and if there’s two of you, one driving and one fiddling, that should overcome the safety issue.
