Squeezing the picture, the horizon is clearly curved. Photo from sailing across the Atlantic Sea. Notice the cloud front going behind the horizon. I was standing on a sail boat approximately 3 meters above sea level. Squeezing the picture, the horizon is clearly curved.
Sadly "this video is no longer available because the account associated with this video has been closed". Have you really deleted all your FE debunking videos? What a loss!
Now we know it in Finland as "Rory's method".
Below are screenshots of a situation where the horizon is clearly below the center of the image. In this case, barrel distortion only reduces the curvature of the horizon, but the curvature is still visible.
These last two posts by Pertti Niukkanen are fascinating, and probably should be broken out of a thread on measuring horizon curvature with a level, both to keep this thread on topic and to give these posts more prominence.
Yes, I should have the horizon in center, however I thought it was close enough to illustrate the curvature + the cloud front going over and behind.That's pretty much a requirement, really. Even if you get it in the center, that does not guarantee that there is no distortion.