Group By
For xbar, s, and R charts your data must be subdivided into groups. The statistic to be charted is calculated within each group, and the variation within each group is used to determine the control limits. If the number of observations within each group is constant, choose Size here, and enter the group size in the Group Size box. If the number of observations varies between groups, you will need to have a column in your data set that identifies the groupings. In this case choose Column here and enter the column name in the Group Column box. If you are using a group column, then observations in a group must appear in consecutive rows, and the group column must have the same value for all rows within each group, but different values for each group.