RE: Need gun selection help, here's why.
The circle thing is useful in determining where thedensest part of the pattern is hitting relative to the point of aim.
Shoot at a specific spot at say 30 yds. Then try to surround the greatest number of hits with a circle of whatever size. Compare the center of the circle to the spot you aimed at to determine whether your gun shoots high, low, left or right. Do a couple times to verify.