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  • $\begingroup$ wtf, why the down vote? $\endgroup$ Commented Oct 21, 2018 at 13:21
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    $\begingroup$ Not mine, but perhaps because the OP asked for local way to show that Earth is globally round, whereas you require that he travel all over the world. On another note, I don't understand your statement "how can a flat earth have a circumference?" That we can measure the circumference is not really a fact to a FE'er (unless you refer to the distance along the "South Pole's Wall of Ice"). I also don't understand why the rotation of the Earth should influence the "average measured value along the equator". You mean because rotation flattens the Earth? $\endgroup$ Commented Oct 22, 2018 at 9:31
  • $\begingroup$ Thank you for your input. So I can understand that first point, however, they themselves do not have to go around to the world.... they could organize a group whose members are located around the world and share their results via the internet. Of course, we're not going to agree on "facts" when talking with a flat earther, but I thought I'd include the point for completion, since a flat earth would not have a circumference along its flat edge... Lastly, yes I do mean that: the rotation of the earth causes the earth the bulge slightly from sphericity at the equator. $\endgroup$ Commented Oct 22, 2018 at 15:56
  • $\begingroup$ Quoting your own answer, "There are many ways to verify that Earth is round, both locally and globally, but I think they all require you to either believe that other people are not a part of a plot (e.g. you'd have to believe that pictures of Earth taken from space are not faked), or to travel a bit (e.g. go to several locations and look at ships/bridges/land disappear below the horizon)." So my answer requires a little bit of travel, but is still a "local" measurement since the measuring of the circumference only requires local phenomena. $\endgroup$ Commented Oct 22, 2018 at 15:58
  • $\begingroup$ Does that make sense? Eratosthenes' measurement is local, but if you do it at a few different places, one can make a global claim about the shape of the earth. $\endgroup$ Commented Oct 22, 2018 at 16:00