A single measureable quality characteristic such as dimension, weight or volume is called a variable. In
such cases, control charts for variables are used. These include ܺത - chart for controlling the process average and
R-chart for controlling the process variability. If the quality related characteristics such as characteristics for
appearance, softness, colour, taste, etc., attribute control chart such as p-chart , c-chart are used to monitor the
production process. Sometimes classified as either “conforming or nonconforming”, depending upon whether
or not they must meet the specifications. The p-chart