Since the EWMA chart performs well in detecting small shifts but does not react to large shifts as quickly as the Shewhart chart. A good way to further improve sensitivity of the control procedure to large shifts without sacrificing the ability to detect small shifts quickly is to combine a Shewhart chart with the EWMA. These combined Shewhart-EWMA control procedures are effective against both large and small process changes. When using such schemes, it may be helpful to use slightly wider than usual limits on the Shewhart chart (e.g., 3.2 sigma is recommended by Montgomery,2001). The reason for this is to prevent the false alarm rate from increasing too much when we add the Shewhart chart.