I second TruckCamper's point. When we took Rosie the '41 ton-and-a-half fire truck to Indianapolis and back, found that the speedo averaged 5 - 10 mph less than the chase car indicated. Though I haven't tested it against mile markers - don't go on the high-way much - I suspect the mileage reading is also incorrect, as I can't see how one could differ from the other. At least the error is a favorable one, ie: getting MORE miles than indicated per fill-up.
Of course, that also means more miles on the truck than indicated . . . Shoot.
-Michael
