Comment by globular-toast
9 hours ago
> In fact I don't know of any other good way of obtaining a straight edge from scratch quickly
A string made taut between two points is surely a better way? And works at much bigger sizes too (people build walls and foundations using this technique all the time). The paper is less useful in practice because any paper you find is probably straight and square anyway.
Still, I had fun thinking about this as I definitely hadn't considered it before.
Over long distances the string will sag in the middle. That's one of the reasons (not the only reason) construction uses lasers today.
It depends what you need that line for -- if you're projecting onto a wall, that sag matters. If you're projecting onto the ground, it doesn't.
Folded paper won't?
If anybody has ever tried folding a very large paper (or, bedsheets, tarps, etc), they'll realize the wisdom of this comment. Our intuition from folding paper on the order of several to tens of centimetres does not scale to arbitrary size and precision. Paper is relatively rigid, but its rigidity is finite and ensuring local-to-global flatness becomes a painstaking endeavour.
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Folded paper has some structure, so not as much?
I have an asterisk in my post addressing that :) Happy to have picqued your mind.
BTW, your method was the method of choice for the surveyors of the Nile, from the Egyptian civilization.
Paper is hi-tech and was not available until much later, and as you mentioned doesn't scale. But if I have misplaced my ruler ...