Buckle up, because I'm about to talk nerdy. This post is all about the two most common marksmanship measurement systems, how to use them, and which one you should use. Be warned, I will be dropping some math on you. I'll be gentle, though.
I've touched on the magic of angular measurements before. Typically, you're going to run into one of two flavors: minutes of angle or milliradians. The quick version of this is to understand that a radian is another way to measure rotation around a point. A milliradian, sometimes called a mil or MRAD, is 1/1000 of a radian.