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Explains why modern ships and planes use knots instead of miles per hour but the explanation they give wpuld only make sense if earth was shaped like a cylinder nkt a flat plane nor a globe, sphere or oblate spheroid
I imagine you can look at a chart and take the starting lat/long, ending lat/long, and do a little sqrt(x**2 + y**2) to get the nautical miles.
You have to use trigononetry because when you are north or south of the equator by a farther amount then moving the same number of degrees east or west results in a smaller arc distance travelled
