I didn’t realise just how important it is to measure scientifically.

My friend is a flat earther and I we often have discussions on "proofs" that the earth is a globe or is flat.

Recently, my friend asserted that he could see the boats in the harbor on an island 20 miles away. According to the standard calculation miles squared x 8 inches, this gives a drop of 267 feet, so you shouldn't be able to see the boats in the harbor.

I then found out that he was viewing this from a bluff which is 60 feet above sea level.

I erroneously thought, that still doesn't make sense, because that still leaves a 200 foot drop. He shouldn't be able to see the boats in the harbor. But after thinking about it and doing more research I figured out that it is normal that he sees the boats in the harbor.

The calculation of the drop is based on a level view from sea level. What is blocking a person's view in this case,is, the curve of the earth, but that "bump" is only 66 feet high (take half the distance square x 8 inches and you get the size of the bump).

As he was on a bluff 60 feet above sea level and he is 6 feet tall, he was looking over the bump, so it is normal that he could see the boats 20 miles away. Also, he wasn't looking in a level line, but unconsciously he was looking down. The best way to avoid this is to attach a level to a plastic tube and look through that.

I think that many people do not pay attention to these details, but as you can see from the example above, those details make a huge difference.