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Comment by srean | Hacker News Reader

Curved creases aside, the fact that folding a piece of paper gives you a straight line is itself quite amazing and deep.

Even if I couldn't trust a cheap ruler, a straight edge is a piece of paper away.

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One of the underappreciated causes and effects of the industrial revolution is the precision that's around us all the time. To make that piece of paper required thousands of precision surfaces, rollers, etc.

And oh how we take it for granted. I recently spent a few minutes trying to make sense of a situation where I was using a corner of a paper for a square. It turned out the piece of paper was not at all square, at least a quarter of an inch out of square!

One important lesson I remember from high school woodworking class ~45 years ago - when using a set square, make your markings twice with the square flipped over in the opposite direction, so if the square isn't accurate you'll get two distinct markings - and for most wood working purposes just splitting the difference by eye will be accurate enough.

But folding any piece of paper will give you a straight line, no?

Sure, this would probably work with nice handmade paper. But you won't necessarily get a clean fold with thicker or uneven paper, and depending on fiber length and distribution you might get waviness or other issues

traditional chinese paper making is way simpler than that, and produces quite reasonably flat papers.

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