Flight times. My favorite. In the "northern hemisphere" they prove a flat-earth and in the "southern hemisphere" they disprove a flat-earth... or so they say. I believe that the closer you are the the rim, and the higher you are in the air, the the more and more you are effected by what I call associative time dilation. To you, it seems like you are on an eight hour flight, and to the observers on the ground, you are on an eight hour flight. But in actuality, time for you is moving much faster than people on the ground. Once you descend, your time-frame aligns with the terrestrial observers and neither is the wiser. Both parties feel like eight hours have passed, but the proximity to the rim of the earth and the height you are flying at, where the atmolayer's protection is the weakest, cause your time to move faster.
I am currently formulating experiments to test this hypothesis.