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Select Range for Average and Control Limits Help

You can select the subgroup (or sample) range on which to base the averages and control limits. For example, you might have 20 samples on a chart but want to base the average and control limits on samples 5 to 15. To demonstrate how this is done, we will use the following dataset:

The X chart for these data are shown below.

The X chart for these data are shown below.

The software treats the data before sample 5 as a split control limit. The range the control limits are based on (from sample 5 on) is shown in the lower right hand corner of the chart.

Setting the range for the average and control limits does make a change to the worksheet containing the data. The starting point of the range has the X value (or first value in a subgroup) underlined. The same is true for the last point in the range.

When the range has been set, the option to automatically update the control limits for the chart is set to No.

You can remove the range by selecting the “Options” in the “Updating/Options” panel of the SPC for Excel ribbon and selecting the chart name. Then change the option for “Automatically Updating of Limits” to yes. See “Changing Chart Options” for more information.

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