Rob
I may have dreamt this up!
Those parallel lines at the top define a measurement, ie) 12 inches or ?, when setting the scope on a predetermined power. Knowing the measurement between a certain part of an animal is 12" or ?, fit that part of the animal between the two lines and bring the scope into focus.
Then read the distance on the scale on the bottom.
Again this idea may have been brought on by a vivid dream or 70+ years of imagination!