The transmission angle for the fourbar mechanism shown above is defined as the acute angle between the velocity difference vector V32 between links three and four and the absolute velocity vector Vout of the output link (link four).
Due to the fact that V32 will always be perpendicular to link three and Vout will always be perpendicular to link four at the three-four connection point, the transmission angle gamma can be found using the following formula:
gamma = theta4-theta3
