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The mechanism is based on a four-bar linkage consisting of slider 1, moving along fixed guides N, bent lever 2, connected by turning pair A to slider 1, and slider 3, turning about fixed axis D. One arm of bent lever 2 moves in slider 3. Added to this linkage is a double guiding element consisting of two sliders 5 and 4 connected together by turning pair E. When slider 1 moves along axis x-x of guides N, the centre of pivot E describes parabola H. Fixed pivot D is placed at the focus of the parabola, axis x-x coincides with the directrix and distances A͞K and D͞L are equal . Parabolas of various sizes can be obtained by adjusting fixed pivot D along slot F of the base and movable pivot A along slot G of link 2.