The lengths of the links comply with the conditions: A͞B=D͞C, A͞D=B͞C, E͞H=F͞G and F͞E=G͞H. The mechanism has two degrees of freedom so that scale 1, in its translational motion, can take any position on board 2. At this, all points of scale 1 describe identical plane paths. If ring member 3 is fixed in any required position, scale 1 has translational motion and its points describe circles of a radius equal to E͞H=F͞G. This enables parallel lines to be drawn in the required direction.
$907$LW,FD$