Select the method or formula of your choice.
In This Topic
Plotted points
Each plotted point, 
, represents the mean of the observations for subgroup, 
.
Notation
| Term | Description |
|---|---|
| xij | jth observation in the ith subgroup |
| ni | number of observations in subgroup i |
Center line
The center line represents the process mean (
). If you do not specify a historical value, then Minitab uses the average from your data, 
, which is calculated as follows:
Notation
| Term | Description |
|---|---|
 | sum of all individual observations |
 | total number of observations |
Control limits
Lower control limit (LCL)
The value of the lower control limit for each subgroup, i, is calculated as follows:
Upper control limit (UCL)
The value of the upper control limit for each subgroup, i, is calculated as follows:
Notation
| Term | Description |
|---|---|
| μ | process mean |
| k | parameter for Test 1 (The default is 3.) |
| σ | process standard deviation |
| ni | number of observations in subgroup i |