A control chart is a graphical tool that displays the variation of a process over time and compares it to predetermined control limits. It can be used to determine whether a sample product is within an acceptable range by checking if the sample values fall within the upper and lower control limits, which indicate the expected variation of the process. If the sample values are outside the control limits or show a non-random pattern, it indicates that the process is out of control and there may be some assignable causes of variation that need to be investigated and corrected. References = CompTIA Project+ Study Guide: Exam PK0-005, 3rd Edition, Chapter 8: Quality Management1; CompTIA Project+ Certification Study Guide, 3rd Edition, Chapter 8: Quality Management2