The lengths of the links comply with the conditions: E͞B=D͞C and B͞C=E͞D, i.e. figure EBCD is a parallelogram linkage. Rigid triangles FBE, GCB and HCD are respectively similar to triangles FGA, GHF and HGA. For any configuration of parallelogram linkage EBCD, triangle AGH retains constant angles at its vertices. 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 turned through constant angles. The mechanism has reversibility since any point, A, G, H or F, can be selected as the centre of similarity.
$855$LW,P$