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S ChartStat > Control Charts > Variables Charts for Subgroups > S
A control chart of subgroup standard deviations. You can use S charts to track the process variation and detect the presence of special causes. S charts are typically used to track process variation for samples of 9 or more, while R charts are used for smaller samples.
By default, Minitab's S Chart command bases the estimate of the process variation, s, on the average of the subgroup standard deviations. You can also use a pooled standard deviation, or enter a historical value for s.
For more information, see Control Charts Overview and Variables Control Charts for Subgroups Overview.
All observations for a chart are in one column: Choose if data are in one or more columns, then enter the columns.
Subgroup sizes: Enter a number or a column of subscripts. If the subgroups are not equal, each control limit is not a single straight line but varies with the subgroup size. If the subgroup sizes do not vary much, you may want to force the control limits to be constant by specifying a fixed subgroup size using S Options > Limits.
Observations for a subgroup are in one row of columns: Choose if subgroups are arranged in rows across several columns, then enter the columns.