@CedricLevasseur @jd Well, if the building you are living in has been built lopsided, then yes, all tries later on to use right angles, water levels, etc, "doing it right" when working in your home are doomed. Starting from putting up some pictures. The usual procedures for that kind of assume that your wall is a level rectangle. And not a trapezoid, where all round cat toys magically roll to one corner.