To clarify, you place the front of the shaft on the item to be measured. The wire is attached to a guide pointer that goes up and down the shaft. The shaft is calibrated in RPM and you extend the wire out and in to find maximum vibration or maximum swing of the tip of the wire and then read the RPM where the pointer is pointing. I agree it is not very accurate.
Yes, we used it on model airplane motors like Fox and McCoy 35s. We were big on water skiing and U control air planes and model boats with tube radio control. What fun living on a bay in south Texas.
Charlie
