http://www.nacactfca.org/Johnston6stride.pdfUse the chart in this document. Your mid mark should correspond to your grip height. If you're on a 15ft pole, you're probably holding at 14'7", so your mid should be at 49'. Once you dial it in, you might be up to a foot out from the prescribed mid
at most, but any farther and you're doing something wrong, like carrying your pole too low or not planting correctly. This is a really great tool for getting the run nailed down and consistent.