The 12.5s rule indicates random error and may also point to systematic error. This rule is applied within the run only. The following figure shows a Levey-Jennings Chart with a data point outside the ±2.5SD limit.
SPC Rules
1-2s
1-3s
1-3.5s
1-4s
1-5s
2-2s
2 of 3-2s
R-4s
3-1s and 4-1s
7-T
N-x Rules
