In the second book Merchant describes three forms of control: control of specific actions, control of results and control of personnel. When knowledge of which specific actions are desirable is excellent, it is always a good thing to control specific actions. When the ability to measure results on important performance dimensions is high, it is always a good thing to control results. When it is difficult to know which specific actions are desirable and when it is difficult as well to measure the results, the optimal control is the personnel control.