Really? You're calling him out for using 4000 instead of 3959?I don't know why you are using 4000 miles since the radius of the earth is less than that.
Geeesh!
Oh, and I calculated the error for a building 2500 feet long is only 1.8". It's 8" for a mile but the error depends on the square of the distance.
If you can see across a 5 mile lake, the curvature error is 16 feet! I can tell from experience this is true - if you look across a lake into a harbor, it looks like all the sailboats have sunk since you can only see the tops of their masts.
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