The repeatability chart is an R chart. For values of the unbiasing constants, go to
Methods and formulas for estimating sigma for R Chart.

The value of the center line for each subgroup, , is calculated as follows:

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

n_{i} | number of observations in subgroup i |

d_{2}(·) | value of unbiasing constant d_{2} that corresponds to the value specified in parentheses. |

σ | process standard deviation |

Each plotted point, *r _{i}*, represents the range for subgroup

The value of the lower control limit for each subgroup is equal to the greater of the following:

or

The value of the upper control limit for each subgroup is calculated as follows:

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

d_{2}(·) | value of unbiasing constant d_{2} that corresponds to the value specified in parentheses. |

n_{i} | number of observations in subgroup i |

σ | process standard deviation |

k | parameter for Test 1 (The default is 3.) |

d_{3}(·) | value of unbiasing constant d_{3} that corresponds to the value specified in parentheses. |