Easy Way to Calibrate
All I do to calibrate my RV speedometer is ask my mother in law. She's knows everything and is always willing to jump in and take over most anything. I just tie a rope around her neck and kick her out the side door on the expressway. Then I count the number of times she bounces before she begins to simply be dragged and multiply it by 4. Unless it's raining, then you multiply by 4 and subtract 6 from your answer.
Bill & Martha more than 42 years.
Traveling with Shih Tzu's Baily, Bella and Maltese Buster. Towing, Golf Cart, Harley or Polaris RZR.