Statistical Process Control (SPC) Resource Center

What Control Charts Look Like

All control charts have four major sections:

  • Information section
  • Data section
  • Graph section
  • Comments section

Major components of a control chart

An area of the control chart that is often overlooked is the Comments section.

  • If your process has gone out-of-control, the notes in this section will give you clues as to why the process went out-of-control.

All control chart graphs have a centerline and upper and lower control limits.

  • The centerline represents the process mean, or grand average, for the process.
  • The upper and lower control limits show the extents of the common cause variation in the process. They approximate plus and minus three standard deviations from the process mean.

Control limits on a control chart.