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Sigma
Chart Calculations
Plotted statistic
The
subgroup standard deviation
where xi are the observations
in subgroup j, x-barj is the subgroup average
for subgroup j, and n is the subgroup size.
Center Line
Average
Sigma
UCL , LCL (Upper and Lower
Control Limit)
where S-bar is the Average
Sigma , c4 is a function of n (available in any statistical quality
control textbook).
Notes: Some authors prefer
to write this as:
where B3 and B4 are a function
of n (available in any statistical quality control textbook).
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