Ah, ok I was managing to miss the meaning of the subtraction step. Whoopsie. Corollary then, how does this equate to a 350 foot tall wall of water? Wouldn't the water follow the curve of the earth? So, if you stood on that beach, looked out along a perfectly level plane (for a perpendicular line) if it was a flat Earth, you would be looking directly at head level of the beach on the other side. If the Earth is round, you would be looking at a point, roughly 350 feet up. Right? What do you see when you do this? The notes in the wiki don't suggest he's using any kind of measuring device, instead implying this 'wall of water' that he can't see (but which shouldn't be there to begin with right?).