How can someone studying a process know whether or not the process is under control? Why is this important?

Question

Quizplus · Accepted Answer

The Answer is A process is under control if the amount of variation present in the process remains constant over time. Process centering must also be constant over time. If both of these are constant, then process behavior is predictable enabling decisions to be made about process performance.

How Can Someone Studying a Process Know Whether or Not