What aspect of quality does a control chart primarily monitor?

A control chart primarily monitors variation in process data over time, which is crucial for understanding the stability and capability of a process. By tracking data points plotted over time against defined control limits, it allows quality engineers to detect trends, shifts, or any out-of-control conditions in the process. This continuous monitoring helps identify when a process may be deviating from its expected behavior, thus enabling timely interventions to maintain or improve quality levels.

Variations can come from various sources, including common cause variation (inherent to the process) and special cause variation (arising from external factors). The primary purpose of a control chart is to differentiate between these types of variations, ensuring that any corrective actions taken are appropriate for the specific situation observed. Effective use of control charts is fundamental in quality management as it directly supports maintaining product quality and process efficiency over time. Understanding how a process behaves regarding variation is key to quality improvement efforts.