Your basic premise is wrong to begin with. Levels do not work 'based on the ground, earth's positon, etc." It works on gravity which is permanently fixed to the center of mass of whatever planet, star, moon, etc. you are on.
Try again but get an education first.
Harry K
------------------------------------------------------------------------ You're correct. His basic premise is VERY wrong. The solar system is definitely NOT level:
The OP should appreciate having a level floor when he next loses his marbles - that way they'll stay in the pretty much the same place.
You're right about gravity. It's a pretty good basis for determing levels. What amazes me is that even though the Greeks clearly knew about levels and how to use them, they built "to eye" in the sense that "level and square" often don't look proportionally correct because of perspective effects.
To counter that effect the Greek builders created optical illusions to make the buildings appear perfect. If steps are built perfectly flat or horizontal, they will seem to sag in the middle. Every horizontal line in Grecian temples therefore curves slightly upwards. If columns are built straight up and down, they will appear to lean outwards. The ancient Greeks built vertical lines to lean towards the middle.
They were quite familar with plumb bobs, ancient ones have been discovered in the rubble of temples that collapsed from earthquakes during construction. They used them, however, to deliberately and precisely build "out of plumb" so that it would look perfectly rectangular from a distance. Quite an idea using levels to deliberately build out of plumb buildings that looked perfect but were far from it, anglewise.
-- Bobby G.