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The lengths of the links comply with the conditions: A͞B=A͞D, G͞B=G͞D, A͞C=A͞E and F͞C=F͞E. Figures ACFE and ABGD are rhomboid linkages. For any configuration of the mechanism, points A, F and G lie on a single straight line. When link 1 turns about fixed axis F, selected as the centre of similarity, and one of the points, A or G, is traced along any arbitrary path, the other point describes a similar path. The mechanism has reversibility since any point, A, G or F, can be selected as the centre of similarity.