folks need to keep in mind that aside from these rigs having 40-60 years of use and abuse, they weren't supplied with scientific grade instruments I'd be surprised if any year speedo was very accurate over it's full range even when new
"When we tug a single thing in nature, we find it attached to the rest of the world" ~ John Muir "When we tug a single thing on an old truck, we find it falls off" ~ me Some TF series details & TF heater pics
folks need to keep in mind that aside from these rigs having 40-60 years of use and abuse, they weren't supplied with scientific grade instruments 
I'd be surprised if any year speedo was very accurate over it's full range even when new