“…Shewhart (1931) proposed a scheme for detecting out-of-control signals and shifts in the mean from its target value 0 μ . Ott (1975), Rocke (1989), Ryan (1989), Chen (1997), Quesenberry (1997), Smith (1998), Maravelakis, et al, (2002), Woodall et al (2004), Montgomery (2005), and several other authors modified and extended the Shewhart control charts. The Shewhart procedure usually is based on at least 20 to 25 sample group sizes ( k ) and at least 4 to 6 sample subgroup sizes ( n ).…”