If it swings back toward the arm rest, that is okay. Just make sure that it is remaining level as it moves. It's not that big of a deal. If you are very slightly off level, it's not going to ruin anything. I just eyeball it myself. I don't use a level or anything like that on the tonearm. I simply put a little bubble level on the TT and level that. Then the arm will be level, when it looks level, by eye. Don't make things harder than they have to be. Just get it where it looks good, and go with it. You'll have to dial in the VTF by ear anyway.
