Two Alternatives to the Shewhart X̄ Control Chart

Average run length (ARL) values are calculated for two X̄ control chart schemes and compared with those of a standard Shewhart chart. Both control charts are based on runs rules and are easily implemented. An out-of-control condition for one of the charts is a run of two of two successive points beyond a special control limit. The other chart uses a run of two of three successive points beyond a different control limit. Both schemes are shown to have better, that is, lower, ARL values than the standard Shewhart chart for process average shifts as large as 2.6 standard deviations from the mean.