p Chart
- Last UpdatedMay 16, 2023
- 2 minute read
The following table contains the formulas used to calculate LCL and UCL for a chart point.
The example in the table illustrates the control limits calculated for a sample size of 15.
|
Formula |
Example |
|---|---|
|
CL = LCL = UCL = where n is the actual sample size from the sample. If LCL < 0, then LCL = 0; otherwise LCL. If UCL > 1, then UCL = 1; otherwise UCL. |
CL = 0.17647 LCL = 0.17647 – (3 * = –0.11882 LCL = 0 UCL = 0.17647 (+ 3 * = 0.47176 |
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The following table shows example control limits calculated for each chart point.
|
Label |
Chart Point (Fraction Defective) |
Count |
Size |
LCL |
CL |
UCL |
Lower σ |
Upper σ |
|---|---|---|---|---|---|---|---|---|
|
1 |
0.13333 |
2 |
15 |
0 |
0.176471 |
0.471762 |
0.058824 |
0.098430 |
|
2 |
0.11111 |
1 |
9 |
0 |
0.176471 |
0.557691 |
0.058824 |
0.127073 |
|
3 |
0.2 |
3 |
15 |
0 |
0.176471 |
0.471762 |
0.058824 |
0.098430 |
|
4 |
0.06667 |
1 |
15 |
0 |
0.176471 |
0.471762 |
0.058824 |
0.098430 |
|
5 |
0.26667 |
4 |
15 |
0 |
0.176471 |
0.471762 |
0.058824 |
0.098430 |
|
6 |
0.3 |
6 |
20 |
0 |
0.176471 |
0.432201 |
0.058824 |
0.085243 |
|
7 |
0.06667 |
1 |
15 |
0 |
0.176471 |
0.471762 |
0.058824 |
0.098430 |
|
8 |
0.2 |
3 |
15 |
0 |
0.176471 |
0.471762 |
0.058824 |
0.098430 |