You could always make your own marks on another stretch of road using another vehicles odometer. Or have someone follow you with walkie talkies and compare odometer readings over a 5 or 10 mile distance and see if there is a discrepancy.
As my long gone father in-law used to always say, "there's more than one way to skin a cat".
This is a really interesting thread, as I am afraid to check the mileage that I am getting with my '59 viking. I am quite sure that it is not very good.
John
