Select the method or formula of your choice.
In This Topic
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
| Term | Description |
|---|---|
| MR | moving 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.
When the average moving range is used to estimate the standard deviation, the center line = MR
When the median moving range is used to estimate the standard deviation, the center line = d2(w) * MR.
Notation
- MR
- the estimate of the average moving range for the method that you use to estimate the standard deviation
- d2(w)
- an unbiasing constant
- 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
| Term | Description |
|---|---|
| d2() | a constant used to estimate the standard deviation |
| w | number 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. |
