You say that this is a large quilt top, so I'm assuming it hasn't already been quilted. I would not do any squaring until after it is quilted. I am like auntpiggylpn; I never square a top. And I seldom square my blocks, unless they're the type that are intentionally made bigger so that they can be cut down. Instead, I TRY to sew each seam accurately, and if the block starts going wonky I TRY to stop and fix it before going any further. If a block doesn't measure right, I don't use it, and I try to figure out what I did wrong so I can fix it on the next block. When I'm quilting the top (on the longarm), I TRY to keep it straight in all directions and not pull it out of alignment. When I'm done, I do check the quilt for squareness. I sometimes need to shave a little off one corner, but not usually.