# Process Capability Indices

## Short-Term Capability
| Index | Formula | Use |
|-------|---------|-----|
| Cp | (USL-LSL)/6σ | Potential capability |
| Cpk | min[(USL-μ)/3σ, (μ-LSL)/3σ] | Actual capability |

## Long-Term Performance
| Index | Formula | Use |
|-------|---------|-----|
| Pp | (USL-LSL)/6σ_total | Potential performance |
| Ppk | min[(USL-μ)/3σ_total, (μ-LSL)/3σ_total] | Actual performance |

## Evaluation Criteria
| Cpk/Ppk | Rating | Action |
|---------|--------|--------|
| ≥2.0 | Six Sigma | Maintain |
| 1.67-2.0 | Excellent | Maintain |
| 1.33-1.67 | Good | Continuous improvement |
| 1.0-1.33 | Marginal | Improvement plan needed |
| <1.0 | Insufficient | 100% inspection required |