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A comment on Hand Scraping a Truly Flat Plane (1908) [pdf]. Parent comment

Re:Hand Scraping a Truly Flat Plane (1908) [pdf] by SECProto on Thursday April 16, 2020 @09:37PM (#22895428)
> Incidentally, this is the real reason manholes were round.

This doesn't pass the sniff test to me. A manhole lid fits loosely in its frame, and is simply cast. The round shape is used ecause that way the lid cannot fall into the hole (frame is a slightly narrower diameter than the lid is in any orientation)

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Re:Hand Scraping a Truly Flat Plane (1908) [pdf] by hombre_fatal on Friday April 17, 2020 @12:23AM (#22896177)
But that works with equilateral polygons as well. How would a square lid fall into a smaller square hole?
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Re:Hand Scraping a Truly Flat Plane (1908) [pdf] by mattclarkdotnet on Friday April 17, 2020 @12:45AM (#22896271)
Diagonally, because the hole is 1.4 times wider diagonally than the cover is on each side
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Re:Hand Scraping a Truly Flat Plane (1908) [pdf] by hombre_fatal on Thursday April 23, 2020 @11:31PM (#22964355)
Me dumb. The hole would have to be much smaller.
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Re:Hand Scraping a Truly Flat Plane (1908) [pdf] by patrickyeon on Friday April 17, 2020 @12:41AM (#22896253)
Diagonally. The length of a side is considerably shorter (1/sqrt(2) times shorter, actually) than the diagonal.
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