In the 1920’s while working at ATT Bell labs, Dr Walter Shewhart (mentor of W Edwards Deming) sought a way to improve telephone transmission systems. Seeking to reduce variations and failures, on May 16, 1924 Dr Shewhart wrote an internal memo introducing the concept of the control chart [Wikipedia]. Today the control chart (AKA process quality control chart or Shewhart chart) has become the standard statistical tool for finding variation that lead to continual improvement. As with other continual improvement tools, the control chart can be understood in a short time, yet takes a lifetime to master as a truly powerful tool for statistical and incremental improvements. The control chart is a tool that tells us whether a process or system is in a state of statistical control. The state of statistical control is one in which a minimum or acceptable amount of variation is acceptable while still meeting the desired output of the process. Shewhart recognized that every process and sys...