Plan a flight route that always flys the same directions on your compass. For example East. Then keep flying in that direction until you end up at your starting point.
The Earth is a flat disk (like the pizza pie) and the compass needle always points to the center (north). This being so, if you travel east or west you will eventually travel in a circle.
We do not have to resort to complex formulas to dispel the theory of a flat plot of land. Just look around and check ten times: the Earth definitely inevitable, completely and absolutely not flat at 100%.
Equally obvious truth is that the Earth, like the rest of the body large enough space is shaped like a ball, we are not questioned. Although religious tales continue fooling adherents of religious belief, the allegations that the Earth is a flat disc