How are control limits calculated for the different Shewhart control charts?
Mean and Range Charts: You can compute the limits in the following ways: • as a specified multiple (k) of the standard errors of X-bari and Ri above and below the central line. The default limits are computed with k=3 (these are referred to as 3σ limits). • as probability limits defined in terms of α, a specified probability that X-bari or Ri exceeds the limits.
