I collect hubodometers which is a device that is attached to the hub of a truck or bus to give an accurate reading of distance travelled.
May have noticed them as that of looking device that appears to stay upright while the wheel is spinning.
I have always had a fascination with looking at them and working out how they are attached to the wheel.a

Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!