The lengths of the links comply with the conditions: A͞D=B͞C and A͞B=D͞C. If the small link AD is fixed, the links will rotate in the same direction. The transmission ratio is i₁ₐ=A͞E/D͞E. Point E is the intersection of the axis of link 2 and line AD. At the extreme positions (dead centres), pins a' and b' of link 2 abut against stops a and b of base 4. As a result uncertainty of motion of the mechanism is eliminated.
$642$LW,CC$