I was putting up some wall decorations earlier today and was painstakingly realigning everything until it looked level to my eyes. It might be just a hair off, but if I don’t correct it, I’ll see the misalignment almost instantly and get bothered for the rest of time until I fix it. Has anyone investigated, or is there literature on the minimum perceptible angle from level to the naked eye?
I can’t find anything at all regarding discussion, study or opinions on the question but I can tell you that it depends on the person and most likely, they’re experience in working at leveling/setting plumb.
Having used levels(spirit, laser, etc.) for decades, I can set an object like a stud, header or a picture for my wife and often don’t need to move it after checking with a level but my wife will often notice that a group of items aren’t leveled the same on a wall but she won’t be sure which one is off. There will usually be a few adjustments to all of them before she’s happy.