This nude was drawn using the optical reduction method which is a very precise way of drawing. The artist finds a location in which his sight sizing tool measures the model at a specific unit size. He then backs up to his easel and sizes that unit of measurement on the paper. The two positions on the floor get taped as well as the easel's position. There is quite a bit of back and forth in this process, so the model must be in a comfortable and (exactly) recreatable pose. The artist must also remember to keep his arms extended (it is easier to reproduce that position) and to mark of the standard unit of measurement that you choose (usually head length) on the sight sizing tool with tape.