You know, I have just never obsessed about being absolutely, perfectly level. Yes, I have levels stuck on the outside for both directions and, yes, I level until comfortable and within a degree or two. I also carry a little 12" carpenter's level. I prefer to be off a little, leaning side to side at a slight angle to assure the shower draining properly. Now, I don't mean four or five degrees, but I have never found harm in a degree or two. I have witnessed folks working for an hour to get a rig level.
Twenty years ago the refrigs were much more sensitive to leveling than they are now. In fact, it was common thirty years ago or so that if a fridge had operated much off plumb it could cause the gas to bubble up and not operate much at all. Same thing back then if the refrig was not operated for long periods of time. The solution was "burping" the refrigerator. Take it out, turn it upside down and shake it a bit. Leave it inverted over night and reinstall. Those, my friends, were the "good ole days". Like nylon tires and butterfly valves in the carbs, I think I will take "modern" most of the time. By the way, refrigs were much simpler back then and smaller, too. Still, burping was a bear.
Paul