Data - U Chart Diagnostic, U Chart, and Laney U' Chart
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You must have at least one column containing the number of defects. Each row of a column should contain the number of defects for one subgroup.

If the subgroup sizes are different, you must also include a column that indicates the size of each subgroup. If the size is the same for each subgroup, you can enter the subgroup size directly in the dialog box instead of providing a column.

Suppose you collect data each day on the number of scratches found per square meter of finished surface. The number of defects is the number of scratches found on a given day. The subgroup size is the number of square meters of surface that was inspected that day. Your data might look like the table below.

Each row in the table represents a single day. The Scratches column indicates the number of defects found that day. The Square Meters column indicates the number of square meters of surface that was inspected that day.

The U Chart and Laney U' Chart divide the number of defects by the subgroup size to calculate the number of defects per subgroup.

The control limits for the U Chart and Laney U' Chart change depending on the size of each subgroup. In general, the control limits are further from the center line for smaller subgroups than they are for larger ones. You can force the control limits and center line to be constant by entering a fixed subgroup size, for example the average subgroup size. See To force control limits and center line to be constant.

When an observation is missing, a gap exists in the chart for that observation.