Term | Description |
---|---|

USL | Upper specification limit |

LSL | Lower specification limit |

Toler | Multiplier of the sigma tolerance (Minitab uses 6 as the default value) |

Overall standard deviation |

Cpm is available only when a target is specified. Minitab calculates Cpm based on known values of LSL, USL, and T.

Known value | Cpm |
---|---|

LSL and USL only | * |

LSL, USL, and T = m | |

LSL, USL, and T ≠ m | |

USL and T only | |

LSL and T only | |

Either LSL or USL only | * |

Term | Description |
---|---|

* | Missing value |

USL | Upper specification limit |

LSL | Lower specification limit |

m | Midpoint between USL and LSL |

T | Target value |

X_{ij} | j^{th} observation in the i^{th} subgroup |

n_{i} | Number of observations in the i^{th} subgroup |

Toler | Multiplier of the sigma tolerance (Minitab uses 6 as the default value) |

The expected number of parts per million that are outside of the specification limits, based on the overall variation of the process, is

Term | Description |
---|---|

PPM | Parts per million |

LSL | Lower specification limit |

USL | Upper specification limit |

Φ (X) | Cumulative distribution function (CDF) of a standard normal distribution |

Average of the observations | |

s | Overall standard deviation |

Benchmark Z statistics for overall capability are calculated by finding the Z value using the standard normal (0,1) distribution for the corresponding statistics.

where:

Term | Description |
---|---|

LSL | Lower specification limit |

USL | Upper specification limit |

Φ (X) | Cumulative distribution function (CDF) of a standard normal distribution |

Φ^{-1} (X) | Inverse CDF of a standard normal distribution |

Overall standard deviation |