X
and R Chartoverview how to example data see also
X
and R ChartStat > Control Charts > Variables Charts for Subgroups > Xbar-R
Displays a control chart for subgroup means (an X chart) and a control chart for subgroup ranges (an R chart) in the same graph window. The X chart is drawn in the upper half of the screen; the R chart in the lower half. Seeing both charts together allows you to track both the process level and process variation at the same time, as well as detect the presence of special causes. See [32] for a discussion of how to interpret joint patterns in the two charts.
X and R charts are typically used to track the process level and process variation for samples of size 8 or less, while X and S charts are used for larger samples.
By default, Minitab's X and 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 Xbar-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.