Help with earth curvature, please

[Guest]

**sorry I posted this in the wrong place, and now reposting here**

Hi everyone,

My brother-in-law is a flat-earther and sent me this video about earth curvature.

Math is not my strong point and I feel a bit bamboozled by it.

I'd like to know if the math checks out on this video: https://www.youtube.com/watch?v=9sou_4f ... jy&index=4

I also want to know if the math checks out at this earth curvature calculator - is it usable? https://earthcurvature.com/

Thank you. Please hold the ridicule and give me the math, baby.

[Guest]

And here is a working link https://www.youtube.com/watch?v=9sou_4f ... jy&index=4