APC, your process autopilot
The autopilot on an airplane assists the pilot in all routine operations, keeping the plane at the altitude, speed, and direction chosen.
In the same way, APC keeps the unit stable and safe in the best operating zone.
As the plane autopilot, it does what an operator would do, but every minute of every hour of every day.
Advanced Process Control (APC) plays the same role at the autopilot on an airplane.