Pattern Rule Detection

Toggle between Western Electric (4 rules), Nelson (all 8 rules), or a custom selection. Default: Nelson Rules enabled. Your preference is saved per characteristic — some characteristics may warrant more sensitive detection than others.

Rule 1: One point beyond 3σ. Rule 2: Nine consecutive points on one side of the center line. Rule 3: Six consecutive points steadily increasing or decreasing. Rule 4: Fourteen points alternating up and down. Rule 5: Two of three consecutive points beyond 2σ on the same side. Rule 6: Four of five consecutive points beyond 1σ on the same side. Rule 7: Fifteen consecutive points within 1σ of the center line. Rule 8: Eight consecutive points beyond 1σ on either side.

Violating points are highlighted with red diamonds. The pattern region is shaded with a semi-transparent overlay connecting involved points. A rule number chip appears next to each violation. Click any violation for the full plain-language explanation with recommended investigation steps.

The system displays the expected false alarm rate for your active rule set. With all 8 Nelson rules active, the expected false alarm rate on an in-control process is approximately 1 per 91 subgroups. This helps you calibrate your response — if you see one violation per 100 subgroups on a stable process, that's expected statistical noise, not necessarily a real problem.