Machine readers can size a blind hole, hand cannot. Hand can be put half way down the taper to provide a force fit. It’s always best to guide a hand reamer using the centre. Hand readers need a smaller reaming allowance to stop them juddering in the hole. I have often used a hand reamer under power, but by pushing the tailstock to give some small measure of float,- not for very small ones though! I’m building a set of both.