The lengths of the links comply with the conditions: A͞D=C͞G, A͞C=D͞G, A͞E=B͞F and E͞F=A͞B, i.e. figures ADGC and AEFB are parallelogram linkages. For any configuration of the mechanism, points G, A and F 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.
$842$LW,P$