Sometimes a standard control chart does not do a good job of displaying information, such as when you want to display an improvement in your process, show multiple processes on one chart, or search for causes of variability in your process. Allowing you to group your data into discrete subgroups of the original retrieval will give you the power to drill down into your data to search out variability and to display process improvements.
The program can use subsets of the retrieved data called "Data Groups" to calculate control limits or generate new charts for each group of data. A set of control limits will be calculated for each data group in a retrieval.
Data Groups can be turned off, manually selected, defined by Anchor points, changes in Traceability, or date/time changes in year, month, day or hour. This option is not available for MINITAB chart windows.
The first subgroup in a data group can be represented on a control chart by a vertical line going through the subgroup. These vertical lines may be turned on or off from the Line Options tab of the Display Options screen. The vertical divider always goes through the first subgroup in a group, and all the data after the line is included in the group up to, but not including the subgroup on next divider.
Although the data on a chart may contain several groups, all of the subgroups are connected. In other words, there will be a line connecting the last subgroup from one data group to the first subgroup in the next data group.
The control limits values displayed on the chart will be those of the last group displayed on the chart
When a chart is first drawn, data grouping occurs according to the Data Grouped on Control and CuSum charts setting for the current configuration. For more information on changing this default setting, see SPC Chart Defaults .
More:
Chart title and statistics list options for grouped data
Viewing details for data groups