# Control Charts Reference

## Variable Control Charts
| Chart | Subgroup Size | Use Case |
|-------|--------------|----------|
| Xbar-R | 2-9 | Most common |
| Xbar-S | ≥10 | Large subgroups |
| I-MR | 1 | Individual values |

## Attribute Control Charts
| Chart | Sample Size | Use Case |
|-------|------------|----------|
| p | Variable | Proportion defective |
| np | Fixed | Number defective |
| c | Fixed | Count of defects |
| u | Variable | Defects per unit |

## 8 Out-of-Control Rules (AIAG-VDA)
1. 1 point beyond 3σ
2. 9 points on same side of CL
3. 6 points trending up/down
4. 14 points alternating
5. 2 of 3 points beyond 2σ
6. 4 of 5 points beyond 1σ
7. 15 points within 1σ
8. 8 points beyond 1σ