depends HEAVILY on the eye. some folks are really good at eyeballing shit. usually this goes hand in hand with other “visual calculus” skills like telling whether two things are the same size or determining angles at a glance.
reckon it’s just spatial reasoning + visualization + practice. i had an uncle who could look at a mechanical system and tell you exactly where all the wear would occur. i always thought it was some kind of savant trick until i started working on similar stuff.
the brain is just another muscle, you can train it to so all sorts of really amazing things!
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