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HallsofIvy said:I disagree with "it originally came about in desire to find the area of a circle". I think there is clear historical evidence that \pi was first used to find the circumference of a circle. Yes, one can easily write that "c= 2\pi r" using [it ex]2\pi[/itex], but if you are talking about a pillar or tree trunk, it is far easier to measure the diameter rather than the radius. That's why 'c= \pi d" is much more natural.
Timber cruisers in the woods of the Pacific Northwest use a tape measure marked in Pi units to measure the diameter of a tree. Just wrap the tape around the tree and read the diameter. At least they were used when there was a active logging industry.