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A compass is an ideal tool for drawing circles.

Hence it can be used according to Euclid's third postulate to construct a circle using any two given points:

$(1): \quad$ the center


$(2): \quad$ an arbitrary point on the circumference.

Also known as

A compass should strictly be called a pair of compasses (using the same idea as a pair of scissors), but this is considered pedantic.

Note, however, that compass is also the word for a navigational aid based upon the north-pointing property of a magnetized needle. If there exists any risk of confusion, then pair of compasses is preferred.

Also see