Needing a tach for setting fertilizer spreader spinner rpm's. There are contact and non-contact. Obviously the contact versions you touch the meter to the center of the shaft. Borrowed one before but that time the shaft had a factory center alignment. On this spreader spinner I have no way of keeping tach dead center. How do the non-contact versions work? Do you have to attach the reflective tape to the side of the shaft? If so how does shaft diameter get accounted for? I can not get directly on the 1" shaft as the spinner is on it and the hub is about 2.5" diameter. I can only guess there is a setting on the tach to account for the shaft diameter.
Only need to very seldom use this tach, any decent cheap recommendations?