The lengths of the links comply with the conditions: A͞B=D͞C and B͞C=A͞D. Link 2 is designed in the form of an arc-shaped slide block which slides along circular guide a-a having its centre at point D. The mechanism is equivalent to the parallel-crank linkage ABCD in which AB and DC are cranks and BC is the connecting rod. At the extreme positions (dead points) the motion of the mechanism becomes uncertain and it may by transformed into a crossed-crank mechanism.
$625$LW,PC$