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instrument for duplicating a motion or copying a geometric shape to a reduced or enlarged scale. It consists of an assemblage of rigid bars adjustably joined by pin joints; as the point of one bar is moved over the outline to be duplicated, the motion is translated to a point on another bar, which makes the desired copy according to the predetermined scale. In the the links 2, 3, 4, and 5 are connected by pin joints at O, A, B, and C. Joint O is fixed to a support, while joints A, B, and C are free to move. Link 5 is a solid bar continuing on to Q. Point P is the guided point and is usually fixed on link 4. As P is guided on a specific path, such as the square in the , point Q will follow a similar path on an enlarged scale. Conversely, if point Q is guided, point P will follow a similar path on a reduced scale