Well, it really doesn't need to be level to gain the lines. Once it is sighted from either end and all four sides have been marked accordingly and the lines snapped connecting the end points it is just as simple as connecting the dots. Yes, put a feather mark in the near center for later use when scribing, if scribing. If you are using snap line rule no need to level it. This doesn't mean you don't have to level it, but it is a unnecessary step.
