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What are the Western Electric Rules for Control Charts?

QI Macros knows the rules so that you don't have to!

Four Western Electric Control Chart Rules.

Western Electric Rules are the original four rules used to interpret control charts. Western Electric Rules can be used with all control charts and are sometimes referred to as WECO Rules.

1. One point above UCL or below LCL
2. Two out of the three points either above or below 2 sigma
   *WECO Rules state that 2 out of 3 points above/below 2 sigma MUST be above OR below the centerline. NOTE: Odd point can be anywhere.*
3. Four out of five 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.

Examples of Western Electric Rules 1, 2, 3 and 4

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Control chart rules available in QI Macros add-in for Excel

QI Macros use Montgomery's Rules as the default. However, you can easily switch to the Western Electric Rules using the QI Macros menu.

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Learn More...

• How to Change Control Chart Rules in QI Macros
• Stability Analysis Using Control Chart Rules
• Westgard Rules

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