The lengths of the links comply with the conditions: B͞C=E͞D and E͞B=D͞C, i.e. figure EBCD is a parallelogram linkage. An additional conditions is that A͞C:C͞H=F͞D:D͞H=A͞B:B͞G. For any configuration of parallelogram linkage EBCD, points A, F, G and H 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, G, H or F, is traced along any arbitrary path, the other two points describe similar paths. The mechanism has reversibility since any point, A, F, G or H, can be selected as the centre of similarity.
$854$LW,P$