Select the method or formula of your choice.

Plotted points

Each data point, MR i , is the moving range of the x values in each group. MR i is not plotted for i < w because it is undefined.

Notation

TermDescription
MRmoving range
w Number of observations in the moving range. By default, w = 2.

Center line

The center line is the unbiased estimate of the average of the moving range.

center line = MR * d2(w)

Notation

MR
the estimate of the average moving range for the method that you use to estimate the standard deviation
d2(w)
the unbiasing constant given in this table
w
the number of observations that are used in the moving range

Control limits

Lower control limit (LCL)

The LCL is the greater of the following:

or

Upper control limit (UCL)

Notation

TermDescription
d2() a constant used to estimate the standard deviation
wnumber of observations in the moving range. By default, w = 2.
σ process standard deviation
k parameter for Test 1 (default is 3)
d3() A constant used to estimate LCL and UCL.
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