To study and demonstrate a quality parameter changes over time, a control chart is used. A control chart has data, a centerline, and two limiting lines – an upper line for the upper control limit (UCL) and a lower line for the lower control limit (LCL). Data are presented usually in time order. If the time gap is equal, the data can be presented in serial order as in Figure 1.
Typical view of the process control chart (generated in MATLAB with the control chart command)