Crank Rocker Mechanism is a four bar linkage. In this linkage, the shortest link rotates fully while the other link pivoted to the fixed link oscillates.
It is a Grashof linkage for which the sum of the lengths of the shortest link and the largest link is less than the sum of the lengths of the other two links.
s + l < p + q
s = length of the shortest link
l = length of the largest link
p and q = lengths of the other two links
In crank rocker mechanism, the link adjacent to the shortest link is fixed. The position of the other three links does not affect the nature of the mechanism.