The lengths of the links comply with the conditions: A͞H=D͞E=C͞B, H͞E=A͞D and H͞B=A͞C. Figures AHBC and AHED are parallelogram linkages. Points F and G of links 2 and 4 lie on an arbitrarily drawn straight line through point A. For any configuration of parallelogram AHBC, points A, F and G lie on a single straight line. When link 1 turns about fixed axis A, selected as the centre of similarity, and one of the points, F or G, is traced along any arbitrary path, the other point describes a similar path. The mechanism has reversibility since any point, A, F or G, can be selected as the centre of similarity.
$844$LW,P$