[userbinator]

The earth is just much much much bigger than in the diagram so the effect is within the margin of error for the measurement he was taking.

It's actually measurable on a human scale:

https://www.mathscinotes.com/2017/01/effect-of-earths-curvat...

1 5/8" difference over 693', or slightly less than 1 part in 5 thousand --- definitely measurable on a smaller scale with accurate machinists' tools.

[pvillano]

One can also watch a boat leaving shore descend "under" the horizon with a telescope

[sigmoid10]

You don't even need a boat or a telescope. Just watch the sun set on the ocean while lying down at the beach just in front of the water. The moment it disappears completely, stand up. You'll see part of it again. If you measure the time it takes disappear completely again and know your own height, you can even get a rough estimate of earth's radius.

[yen223]

Unless I'm picturing it wrong, wouldn't this still happen even if the world were flat?