The lengths of the links comply with the conditions: B͞F=F͞D=D͞E=B͞E=a, A͞F=A͞E=b and A͞C=C͞B. When link 1 turns about fixed axis C, point D travels along straight line q-q which is perpendicular to AC. The mechanism always satisfies the condition: A͞B×A͞D=b²-a²=const. The polar equation of straight line q-q is A͞Dcos(α)=(b²-a²)/(2A͞C)=const. Directions AD and FE are always mutually perpendicular.
$701$LW,GI$