The repeatability chart is an R chart. For values of the unbiasing constants, go to
Methods and formulas for estimating sigma for R Chart.
In This Topic
Center line
The value of the center line for each subgroup, 
, is calculated as follows:
Notation
| Term | Description |
|---|---|
| ni | number of observations in subgroup i |
| d2(·) | value of unbiasing constant d2 that corresponds to the value specified in parentheses. |
| σ | process standard deviation |
Plotted points
Each plotted point, ri, represents the range for subgroup i.
Control limits
Lower control limit (LCL)
The value of the lower control limit for each subgroup 
is equal to the greater of the following:
or
Upper control limit (UCL)
The value of the upper control limit for each subgroup 
is calculated as follows:
Notation
| Term | Description |
|---|---|
| d2(·) | value of unbiasing constant d2 that corresponds to the value specified in parentheses. |
| ni | number of observations in subgroup i |
| σ | process standard deviation |
| k | parameter for Test 1 (The default is 3.) |
| d3(·) | value of unbiasing constant d3 that corresponds to the value specified in parentheses. |
