Western Electric Rules for Control Charts

WECO Rules - the Original Four Rules

Western Electric RulesĀ are the original set of four control chart rules. Western Electric RulesĀ can be used with all Excel control charts and are sometimes referred to as WECO Rules.

Western Electric Rules are Available in QI Macros

western electric control chart rules

List of the Original Four Western Electric Rules

1. One point above UCL or below LCL
2. Two points above/below 2 sigma
3. Three out of four points above/below 1 sigma
4. Eight points in a row above/below the center line

These were expanded by Nelsons Rules in the 1950s.

Western Electric Rule 1: One point above UCL or below LCL

control chart example of Western Electric rule 1

Western Electric Rule 2: Two points above/below 2 sigma

control chart example of Western Electric rule 2

Western Electric Rule 3: Three out of four points above/below 1 sigma

control chart example of Western Electric rule 3

Western Electric Rule 4: Eight points in a row above/below the center line

control chart example of Western Electric rule 4

How to Change to Western Electric Rules in QI Macros

QI Macros use Montgomery's Rules as the default. However, you can easily switch to the Western Electric Rules using the QI Macros menu. See How to Change Control Chart Rules in QI Macros

change control chart stability rules

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