Well, I never wanted to be considered square but I've discovered you really want to be square while constructing a trailer.
Last night we discovered we went out of square by a 1/4 of an inch. This morning we found the problem, fixed in and we were square once again. Then later in the day we removed a couple of interior braces, foolishly thinking we had enough support up...NOT! By mid afternoon we were no longer square. We put the braces back up, added another one and continued to work.
As we packed it in for the night, I didn't check if we were still square, I figure a good night's sleep was in order.
So, the last time we checked we were still square and we shouldn't have gone out, but who knows.
Basically we've come to the conclusion, right angles and levels are our friends.

Lynn & Paul