A control chart is a graph used to study how a process changes over time by plotting data points in time order. It has a central line for the average, and upper and lower control limits determined from historical data. By comparing current data to these lines, you can determine if a process is in or out of control. Control charts are used for controlling ongoing processes, predicting expected outcomes, determining process stability, and analyzing patterns of variation from special or common causes. The basic components are a centerline, lower and upper control limits, and performance data plotted over time. The basic procedure is to determine the time period, collect and plot data, and look for out of control signals to investigate and document the cause and correction.