While trying to fit kitchen units I noticed that the wall is not completely vertical. It's leaning back and losing about 2.5mm for every 100mm up, which is fairly slight but means across the height of a cabinet I'm not flush at the top by about 2cm, which is really annoying. I've seen people get around this with shims but I'd rather just get the wall level if at all possible. Are there any particular tips/techniques on how to level out this kind of discrepancy on a wall? The wall itself is plaster on brick.