Re: What it "shooting the box"?
It's testing the tracking of a scope, in most cases people make the adjustments and shoot in a Square making sure the scope returns to zero and tracks properly.
I use more of a right angle, and you can see a poor representation of one on home page if you watch the Super Sniper Video posted there, I show how I add the reference points, measure in the scope and then shoot. But some just measure and make a pretty square box.
The limitation is, you have to move a lot in order for errors to show, a lot of people will run a box test using less than a 10" square box and many errors won't appear beyond shooter error until well past 20".