Easy way to prove whether the earth is round or flat is to travel to the salt flats of Nevada or Utah and locate a significantly long stretch of flat equally elevated land with point A at one end and point B at the other. Then set a laser at a specific height off of the surface at point A and a receiving surface at point B. If the laser does not impact the receiving surface at the height it was sending from then we have a round earth. If it impacts dead on then we have a flat earth.