When Nearly Flat Isn’t Really Flat

From where I am sitting, the earth is flat. The floor that runs the length of the unit my hackerspace sits in is flat, the concrete apron behind it on which we test our Hacky Racers is flat, and a few undulations in terrain notwithstanding, it remains flat as I walk up the road towards Stony Stratford.

This is a companion discussion topic for the original entry at https://hackaday.com/2023/12/06/when-nearly-flat-isnt-really-flat/