Statistical Process Control (SPC) Resource Center

What are Control Charts?

What are Control Charts?

  • Control charts give a statistical signal that a process has gone out-of-control so the operator can make the necessary adjustments to bring the process back into control.
  • The chart itself can’t control the process. The control chart provides a signal so the operator can take action on the process.
  • A process that is stable is in-control. If the process changes, we get a signal from the control chart that it has gone out-of-control.
  • Adjusting a process when it is not statistically out-of-control is considered over-adjustment and results in increased process variation.
  • Control charts can be used to measure product characteristics or in-process parameters.
  • Measuring an in-process parameter is the best way to monitor a process because it may provide a signal that the process is going out-of-control before bad product is made.

Control Charts give a statistical signal when the process has changed.