A calculator. Or, for a very long time, pencil and paper.

]]>ajay: *I would say that "huge pair of calipers" qualifies as rather more equipment than "bit of string".*

Ajay, you are missing the point. You don't need the calipers to figure out the diameter. You can do it by figuring out the circumference, and then doing math. The string is sufficient. As MattF says, "you could always measure the circumference and divide by pi". No equipment needed. Which, as I said, doesn't change that it's easier to just not do the math and stick with circumference (I agree with you there), but, nonetheless, if you can measure the circumference, you can figure out the diameter with math.

]]>I would say that "huge pair of calipers" qualifies as rather more equipment than "bit of string".

]]>]]>One Circular Mil is a unit of area equal to that of a circle .001" in diameter (.0005" radius). The actual area of a Circular Mil is:

A =Pi x r²

A = 3.14159 x (.0005)² inches

A = .0000007857 square inches

Yes. Is that easier or more difficult, would you say, than measuring the circumference and not dividing by pi?

*On measuring circumference v. diameter, I imagine that for large, somewhat squishy things like ropes, wrapping a string around it is more accurate than pinching it in a caliper. *

Also a good point.

]]>On measuring circumference v. diameter, I imagine that for large, somewhat squishy things like ropes, wrapping a string around it is more accurate than pinching it in a caliper. For tiny metal surgical instruments, I imagine the reverse is true. But perhaps that wasn't the case when Charrière invented his measurement scale.

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