Methods for Estimating the Standard Deviation

When control limits are determined from the input data, three methods (referred to as default, MVLUE, and RMSDF) are available with the MCHART statement for estimating the process standard deviation . The method used to calculate depends on whether you specify the STDDEVIATIONS option in the MCHART statement. If this option is specified, is estimated using subgroup standard deviations; otherwise, is estimated using subgroup ranges. For further details and formulas, see Methods for Estimating the Standard Deviation.