so you use a pencil or charcoal to do that.. i don't get it.
i bought george B. Bridgman's book on drawing from life and it tells you to hold the pencil/charcoal between your fingers and thumb(how so? the thumb vertically or horizontally?)
then it says use the first finger (index finger i guess?) and the pencil/charcoal to mark the extremities of the measurement.
i don't get how it works..how does it work?