1) what the others said, in a gravity well it depends on height above the floor, but not in an accelerating elevator; this limits the height according to the se

1) what the others said, in a gravity well it depends on height above the floor, but not in an accelerating elevator; this limits the height according to the sensitivity of your instruments 2) additionally, we do not know of any disc-shaped objects of sufficient density and matter distribution to produce a uniformly linear gravity field; only galaxies come close but their gravity is small compared e.g. to that of Earth. Most of the time gravity is caused by spherical objects, meaning the lines of the fields diverge. If you had an elevator with a sufficiently large, completely flat floor, you could tell that you're hovering above a planet by observing that a plumb bob forms different angles with different (perfectly upright) walls of the cabin.