The Grashof Condition is used when analysing kinematic chains. The Grashof's law or condition states that "For a four-bar mechanism, the sum of the shortest and longest link lengths should not be greater than the sum of two remaining link lengths".
For a four-bar linkage, the Grashof Condition is satisfied if S+L ≤ P+Q where S is the shortest link, L is the longest, and P and Q are the other links. When the Grashof condition is satisfied, at least one link will be completely rotatable.