YouTube video creator, D Marble, uploaded a video saying he was going to 'prove' that the Earth was flat by taking a spirit level on a flight across the U.S.A.
His theory? That if the Earth is round, the pilots would have to steer the nose of the plane downward, which he would be able to measure on his spirit level. He filmed the level and claimed that because the plane remained level the whole flight the Earth must be flat.
While he clearly thinks he has hard proof that the Earth is flat, the general public proved harder to convince:
Check it out for yourself: