control chart

A control chart is a graphical tool used in industrial statistics and quality management. On the chart, each point corresponds to the value of a statistic—mean, range, proportion of non-conforming items, etc.—calculated from a sample taken at a particular point during a manufacturing process. The x-coordinate of each point represents the sample number or date, and the y-coordinate the observed value of the statistic. Upper and lower control limits are drawn on the chart; when a point exceeds these limits, it signals a potential drift in the process, triggering corrective action.