Yes, it’s from a book called “Uncle John’s Bathroom Reader” and that book was resting on a closed toilet seat in a nation that only kind of uses the metric system in certain situations… however, you’d be surprised how much you can learn after a single visit to any local fast-food joint!
So how the hell was it done? Long piece of rope? Hot air balloon? Or having a bird fly from one point to another and timing it?
Calculations. In 240 BCE, Eratosthenes used a stick. He basically found a place where the sun was directly overhead, and measured the shadow from a stick a known distance to the north of that location. He approximated the circumference of the earth to be 25,000 miles, which was off by 99 miles.
How do we know the conversion of whatever length unit he was using, in modern units?
Uhh, educated guesses. The stadion wasn’t exactly standardized. Most of the conversions I see put 10 stadia at 1 mile so that’s what I went with.
https://en.wikipedia.org/wiki/Stadion_(unit)
The main thing is his methodology was precise.