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.