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RCHART Statement |
The following notation is used in this section:
process standard deviation (standard deviation of the population of measurements) | |
R_{i} | range of measurements in i^{ th} subgroup |
n_{i} | sample size of i^{ th} subgroup |
d_{2}(n) | expected value of the range of n independent normally distributed variables with unit standard deviation |
d_{3}(n) | standard error of the range of n independent observations from a normal population with unit standard deviation |
D_{p}(n) | 100p^{ th} percentile of the distribution of the range of n independent observations from a normal population with unit standard deviation |
The following table provides the formulas for the limits:
Table 39.21: Limits for R ChartsControl Limits |
LCL = lower limit |
UCL = upper limit = |
Probability Limits |
LCL = lower limit |
UCL = upper limit |
The formulas assume that the data are normally distributed. Note that the control limits vary with n_{i} and that the probability limits for R_{i} are asymmetric around the central line. If a standard value is available for , replace with in Table 39.21.
You can specify parameters for the limits as follows:
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