The lengths of the links comply with the conditions: B͞C=E͞D and C͞D=B͞E, i.e. figure BCDE is a parallelogram linkage. Point A of link 1 lies on a straight line passing through points F and G of links 4 and 2. For any configuration of parallelogram linkage BCDE, points A, G and F lie on a single straight line. When link 4 turns about fixed axis F, selected as the centre of similarity, and one of the points, G or A, is traced along any arbitrary path, the other point describes a similar path.
$848$LW,P$