What is Control Chart?

Control Charts:

Control Charts are the graphic devices for detecting variation in the production process and determining the permissible limits of variation. Control charts are based on the theory of probability and theory of sampling. Control charts consists three horizontal lines: central line, upper control limit, and lower control limit.

 Central Line (CL):

Central line is a middle line of the control chart which indicates the grand average of the sample data. It is generally drawn as bold line.

Upper Control Limit (UCL):

Upper control limit is the upper line of the control chart which is usually obtained by adding the 3-sigma to the process average. This line indicates the maximum permissible limit of variation in process. It is denoted by mean + 3σ. It is drawn as dotted line.

Lower Control Limit (LCL):

Lower control limit is the lower line of the control chart which is usually obtained by subtracting the 3-sigma from the process average. This line indicates the minimum permissible limit of variation in process. It is denoted by mean - 3σ. It is drawn as dotted line.

The general format of control chart is presented below;