If S is the smallest link, L is the largest link and P,Q are the intermediate links, then there will be at least one link which will be able to revolve/ rotate if [ S + L < P + Q ]. The four bar mechanisms that satisfy this criteria, are known as grashofian mechanism. For grashofian mechanism, if S is the ground link, then it is double crank mechanism. Here, S = 5, L = 10, P = 8, Q = 9; S + L = 15 which is less than P + Q = 8 + 9 =17 and S = 5 is the ground link.