When link 1 turns about fixed axis A, point E of link 2 travels along path q-q which is approximately a straight line under the condition that point B describes a circular arc approximately coinciding with the elliptic path it would have if points B and C of link 2 travelled exactly along straight lines. The accuracy with which the path of point E approximates a straight line increases with the lengths A͞B and D͞C of links 1 and 3.
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