My wife told me my floating shelf install was 'a little off' and she was totally right
I put up a set of three floating shelves in our living room last month, using a stud finder and a level. I stepped back and thought they looked great, perfectly straight. My wife came in, tilted her head, and said, 'Honey, the middle one is about a quarter inch higher on the right side.' I argued at first, but when I got out the laser level, she was spot on. I had only checked the front edge, not the back where the wall wasn't perfectly flat. I had to take it down, shim the mounting bracket with a few washers, and redo it. Now I always check for level in at least two spots along the length of any shelf or cabinet. Has anyone else had a wall that wasn't flat totally throw off a project like this?
Actually, you need to check the level first. If the wall itself is out of plumb, your level will show that right away. Checking the wall first assumes the wall is straight, which is the whole thing you're trying to find out. Starting with the level is the basic move.