compass divider

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Device, precision tool for measuring, transferring, and marking off lengths, consisting of two straight adjustable arms hinged together and ending in sharp tips. It serves primarily in drafting for accurate dimension transfer from a measuring scale and in machine shops for inscribing lines on surfaces, typically machined, with dimensions taken directly from a ruler. A compass essentially functions as a device where one tip has been replaced by a pencil or other marking instrument. The compass is useful for drawing circles or arcs of circles; it usually features a scale to indicate the radius of the circle being drawn.