The lengths of the links comply with the conditions: A͞B=C͞D and B͞C=A͞D, i.e. figure ABCD is a parallelogram. Slider 2 moves along fixed guides a-a whose axis x-x is at a distance of e from point A. This is the offset of the mechanism. When crank 1 rotates about fixed axis A, slider 2 reciprocates along axis x-x and link 3 oscillates about axis A, always remaining parallel to connecting rod 4.
$1509$SC,6L$