Enricks said: Yes, sorry for my slip of tongue there: I meant eye level. I found that odd because at sea level the "drop" should be 0, like you showed in your "horizon dip" demonstration, so both the horizon and the pole should not show any drop. I don't know if I'm misunderstanding something (almost certainly yes lmao). Click to expand...

The side to side visual "drop" of the horizon is zero at sea level. But that's a totally different thing to the curve of the Earth away from you.And here the telescope is not at the water level. It's like 12 feet above the water, looking at things that are 3 and six miles away. The thing 3 miles away will be 6 feet below the horizontal plane passing through the telescope, and the thing 6 miles away will be 24 feet below that plane.The key thing though is the "bulge", which is 6 feet over 6 miles. i.e. the middle marker will be six feet higher than a line of sight between the end points (assuming all are the same height above the water)