 The distinguishing feature of the PID controller is the ability to use the three "control terms" of proportional, integral and derivative influence on the controller output to apply accurate and optimal control.The block diagram on the right shows the principles of how these terms are generated and applied.It shows a PID controller, which continuously calculates an "error value" formula_1 as the difference between a desired setpoint formula_3 and a measured process variable formula_4, and applies a correction based on proportional, integral, and derivative terms.