Western Electric Company (WECO) Rules

This page is designed to give a probability plot of the time to signaling an alarm (the run-length), for a Shewhart control chart with or without supplementary run rules.

Tell me more about control charts and WECO rules.

Enter your process parameters:
Size of process shift The size of shift that you want to detect, in standardized units. Between 0 and 5
Rule to apply No rule
2 of the last 3 points fall in [-3,-2] or [2,3]
4 of the last 5 points fall in [-3,-1] or [1,3]
8 consecutive points fall on one side of the center line

Create your own rule: consecutive points fall in zone   ± [ , ]
Each rule states an event that causes the plot to signal an alarm. Create your own rule:  ± [2.5, 3] means between [-3, -2.5] or [2.5, 3]
Maximal run length value The largest value that should be on the probability plot