Nelson (1985), provided (8) tests to detect patterns on control charts based on 3*sigma control

limits; Each "zone" - A, B, C - is one sigma wide and x- represents the process mean.

Test 1: 6 points in a row steadily increasing or Test 2: 14 points in a row alternating up and down decreasing UCL C F ICL LCL Test3: 2 out of 3 points in Zone C or beyond Test 4: 4 out of 5 points in a rowin Zone B or C UCL Ual- C A A B LCL Test 5: 15 points in a row in zone A near Xbar Test 6:9 points in a row in zones B/C on both sides of the centerline UCI UCL- C F LCL LCL