Quality and Process Methods • Control Chart Builder • Control Chart Types • Shewhart Control Charts for Variables
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Shewhart Control Charts for Variables
Control charts for variables are classified according to the subgroup summary statistic plotted on the chart.
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X-charts display subgroup means (averages) and are referred to as location charts.
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R-charts display subgroup ranges (maximum – minimum) and are referred to as dispersion charts.
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S-charts display subgroup standard deviations.
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Presummarize charts display subgroup means and standard deviations.
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Individual Measurement charts display individual measurements.
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Moving Range charts display moving ranges of two successive measurements.
Note: If you remove a dispersion chart or turn off the preference Show Two Shewhart Charts, you'll see only the location chart. Any associated scripts will contain the JSL option Show Two Shewhart Charts set to off (0).
XBar-, R-, and S- Charts
For quality characteristics measured on a continuous scale, a typical analysis shows both the process mean and its variability with a mean chart aligned above its corresponding R- or S-chart.
Individual Measurement Charts
Individual Measurement charts displays individual measurements. Individual Measurement charts are appropriate when only one measurement is available for each subgroup sample. If you are charting individual measurements, the individual measurement chart shows above its corresponding moving range chart. Moving Range charts displays moving ranges of two successive measurements.
Presummarize Charts
If your data consist of repeated measurements of the same process unit, you can combine these into one measurement for the unit. Pre-summarizing is not recommended unless the data have repeated measurements on each process or measurement unit.
Presummarize summarizes the process column into sample means and/or standard deviations, based either on the sample size or sample label chosen. Then it charts the summarized data based on the options chosen in the window.
Levey-Jennings Charts
Levey-Jennings charts show a process mean with control limits based on a long-term sigma. The control limits are placed at 3s distance from the center line. The standard deviation, s, for the Levey-Jennings chart is calculated the same way standard deviation is in the Distribution platform.

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Help created on 7/12/2018