The lengths of the links comply with the conditions: B͞C=E͞D and E͞B=D͞C, i.e. figure EBCD is a parallelogram linkage. An additional condition is that A͞C:C͞F=H͞E:E͞G=A͞B:B͞G=H͞D:D͞F. For any configuration of parallelogram linkage EBCD, points A, G, F 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, F or H, is traced along any arbitrary path, the other two points describe similar paths. The mechanism has reversibility since any pioint, A, G, F or H, can be selected as the centre of similarity.
$833$LW,P$