Select the method or formula of your choice.

Plotted points

Each data point, si, is the standard deviation of subgroup, i.

Center line

The center line represents the average standard deviation for a subgroup.

If you do not use an unbiasing constant, then Minitab uses the process standard deviation, σ:

If you use an unbiasing constant(default), then Minitab calculates the center line value for each subgroup, i, as follows:

Notation

TermDescription
σprocess standard deviation
c4()value of the unbiasing constant c4 that corresponds to the value that is specified in parentheses.
ninumber of observations in subgroup i

Control limits

If you do not specify a historical value for the process standard deviation, σ, then Minitab estimates σ from your data using the specified method.

Lower control limit (LCL)

If the unbiasing constant is used:
If the unbiasing constant is not used:

Upper control limit (UCL)

If the unbiasing constant is used:
If the unbiasing constant is not used:

Notation

TermDescription
c4()value of the unbiasing constant c4 that corresponds to the value that is specified in parentheses.
ninumber of observations in subgroup i
σprocess standard deviation
c5()value of the unbiasing constant c5 that corresponds to the value that is specified in parentheses.
kparameter for Test 1. The default is 3.
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