The lengths of the links comply with the conditions: B͞C=E͞D and C͞D=B͞E, i.e. figure BCDE is a parallelogram linkage. Point F of link 4 lies on a straight line passing through points A and G of links 1 and 2. For any configuration of parallelogram linkage BCDE, 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.
$846$LW,P$