Select the method or formula of your choice.
In This Topic
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
| Term | Description |
|---|---|
| σ | process standard deviation |
| c4() | value of the unbiasing constant c4 that corresponds to the value that is specified in parentheses. |
| ni | number 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
| Term | Description |
|---|---|
| c4() | value of the unbiasing constant c4 that corresponds to the value that is specified in parentheses. |
| ni | number of observations in subgroup i |
| σ | process standard deviation |
| c5() | value of the unbiasing constant c5 that corresponds to the value that is specified in parentheses. |
| k | parameter for Test 1. The default is 3. |
