Control chart, also known as control chart, is a chart designed by statistical method to measure, record and evaluate the quality characteristics of the process, which is used to monitor whether the process is under control. There are center line (CL), upper control line (UCL) and lower control line (LCL) on the graph, and there is a tracking sequence of sample statistics extracted in time sequence. UCL, CL and LCL are collectively referred to as control lines. The center line is the average of controlled statistical values, and the upper and lower control limits are several standard deviations from the center line. Most manufacturing industries use triple standard deviation control boundaries, and other control boundaries can be used if there is sufficient evidence. If the tracking points in the control chart fall outside UCL and LCL, or the arrangement of tracking points between UCL and LCL is not random, it indicates that the process is abnormal.