This is an interesting and fun class exercise but the results were much worse than I expected. I'm reminded of Carl Sagan's Cosmos where he explains how Eratos

This is an interesting and fun class exercise but the results were much worse than I expected. I'm reminded of Carl Sagan's Cosmos where he explains how Eratosthenes calculated the radius of the earth, to a great degree of accuracy, by comparing the shadows of two distant obselisks. I wonder if there is a modern equivalent that would give similar accuracy by observing side-effects of our telecom architecture, or our other very futuristic systems in comparison to Eratosthenes' obelisks.