The Westgard Rule R4s applies to controls within a run (and not between runs).
- If two controls exceed 4SD (that is if one control exceeds +2SD and the other control [or additional control, if more than 2 controls are tested] exceeds -2SD), the run should be rejected.
- This is the case on day 13, as seen on the normal and abnormal L-J QC charts on the right.
