The below table describes the most commonly used control charts. | Type of Chart | Description | Formula | | P-Chart | Classification Data |  | | c-Chart | Count data | 
| | u-Chart | Count Data |  | | X-Chart | Variable Data |  | | S-Chart | Variable Data |  |
The most common Western Electric rules to identify special causes: - any points outside the control limits
- A run of 8 or more points all above or below the center line
- A trend of 6 or more points up or down
- Two out of 3 points near a control limit
- Fifteen points close to the center line
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