My Garmin GPS has a very accurate MPH reading included in its functions. If you have access to one, make up a comparison chart every 10 MPH to provide to your speedo shop, and they can make an adapter that will be as accurate as possible.
Jerry


"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!