The thumbwheel on the brass part zeros the vernier. You still have to remember where you start from. In that position, you would zero on 0 or 1". In the middle somewhere, pic a whole number or build in your total move so you end on a whole number. I want to say the top rod on mine goes full length but I may be mi-remembering and it isn't on there at the moment. I nabbed that pic from the net
