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Individual X Chart Calculations
Plotted statistic
The
observation
Center Line
the
Average (Normal Distribution)
the Median
of the Fitted Distribution (Non-Normal Distributions)
UCL , LCL (Upper and Lower
Control Limit)
The upper control limit for
the observations selected for analysis.
(Normal Distribution)
(Normal Distribution)
where x-bar is the average
and sigma-x is the process
sigma .
Notes:
- Some authors prefer
to write this as:
- For Non-Normal
distributions, the UCLx is set to the percentile of the fitted distribution
corresponding to the ordinate value for the Normal distribution. For
example, the UCL for 3-sigma limits is defined at the 99.865 percentile
of the fitted curve, and the LCL is defined at the 0.135 percentile
of the fitted curve.
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