I took a shotgun class today from a retired LEO. In his career, he was a leader of a SWAT team and the Chief of Police in a south Florida city.
The question that I did not really understand was how to "pattern" a shotgun.

If you already know the answer to this question; then what if you have multiple shotguns...can you remember the pattern of each shotgun you own? If the answer is no, I have a suggestion; if the answer is yes, please explain to us how.