The document discusses the components and characteristics of a PID controller. A PID controller uses proportional, integral and derivative actions to control process variables. The proportional action depends on current error. The integral action depends on accumulated past errors to eliminate steady-state error over time. The derivative action predicts future errors based on the current rate of change to improve stability and reduce overshoot. Together these three actions allow a PID controller to control processes very well without overshoot or undershoot by setting the optimal P, I, and D values for the specific application.