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A conspiracy theorist says he has proved the earth is flat after taking a spirit level onto a plane.

American Flat-Earther D Marble, who describes himself as a "realist", was confident that a pilot would have to dip the nose of an aeroplane to compensate for the curvature of the Earth if the world was really a sphere.

He filmed himself with a spirit level on a flight from North Carolina to Seattle to see if the bubble would move, and has argued that the fact it didn't move must mean the world is entirely flat and not a "spinning ball".

In the YouTube video , D Marble encourages other Flat-Earthers to buy a spirit level from their local hardware store and join his experiment.

(Image: D. Marble/Youtube) (Image: D. Marble/Youtube)

He said: "If we're living on a spinning ball, or a globe, thats 25000 miles in circumference around the equator, according to curvature math the plane should be constantly tipping its nose forward in order to compensate for the curvature regularly during flights.

"But I don't know anyone who's actually reported that happening and thus far it's just been speculation.

"So what I'm going to do, I'm going to take my spirit level onto the plane and prop it to a point where it's level and I'm going to record the fact that the bubble stays perfectly centre."

True to his word, D Marble does exactly that and is clearly delighted with the results of his test, which took place in June and has remained popular on social media.

(Image: D. Marble/Youtube) (Image: D. Marble/Youtube) (Image: D. Marble/Youtube)

At the end of the video , and while still on board the aeroplane, he gives the camera a knowing look and whispers: "It's flat. The Earth is flat."