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R ChartStat > Control Charts > Variables Charts for Subgroups > R
A control chart of subgroup ranges. You can use R charts to track process variation and detect the presence of special causes. R charts are typically used to track process variation for samples of size 8 or less, while S charts are used for larger samples.
By default, an R chart bases the estimate of the process variation, s, on the average of the subgroup ranges. 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 R 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.