What is a Control Chart

A control chart is a graph to monitor a production process. The control chart includes a horizontal line through the middle of the chart representing the process norm or average. It also has a line below this center line representing a lower control limit and a line above it for the upper control limit. Samples are taken periodically and plotted on the graph. If an observation is outside of the upper or lower control limits on the graph, it may indicate that something is wrong in the process; that is, it is not in control. By monitoring the production process with a control chart, the worker and management can detect problems quickly and prevent poor-quality items from passing on through the remainder of the process, and ending up as defective products that must be thrown away or reworked, thus wasting time and resources.