The rights and wrongs of control charts

Few managers of manufacturing processes have the understanding of variability that Deming and other quality experts regard as essential for survival. Lacking this understanding they may attempt to follow a ‘standard procedure’ when setting up control charts. Although this leads to better control and quality improvement in many cases, it is certainly not always successful. Data from two, very different, manufacturing processes are considered. The reasons for failure are examined and suggestions are made for improving the standard procedure.