The lengths of the links comply with the conditions: A͞D=B͞C and A͞B=D͞C, i.e. figure ADCB is a parallelogram linkage. Rigid triangles FDA and ABG are similar. Links 4 and 5 turn about fixed axis C which is the centre of similarity. When point F is traced along any arbitrary path, point G describes a similar path, turned through constant angle ∠FCG=α. The similarity factor k of the pantograph equals k=C͞E/C͞G.
$839$LW,P$