Making requirements known and then responding to them under the guidance of feedback is not a one-time occurrence. If feedback is to be useful, whether it concerns outcomes or behavior, it must be timely and ongoing. Feedback regarding the actual position of the gun mount must arrive in time to keep it aligned with its currently ordered position, not some past position. This, in turn, implies monitoring and measuring the gun mount's actual position and communicating this information to the controller so as to continuously generate the error signal necessary to keep the gun mount in motion and in correspondence with its ordered position. And Desirable Owing to continuously changing conditions and requirements, to the fact that orders always precede the response to them, and to the fact that a body in motion tends to remain in motion, a gun mount is never in perfect alignment with its ordered position.
Error is always present in any dynamic system.
Because error is always present, there is a need not just for standards, but also for tolerances, for some acceptable margin of error regarding performance. Not only is error always present, its presence is essential to the proper functioning of a dynamic system. With no error signal, the gun mount would not move, it would remain wherever it happened to be. Error is essential if things are to change. Thus, error-free performance is not only unattainable but a certain amount of error is necessary to the proper functioning of the system.