To use historical values for the mean
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With U Chart, Laney U' Chart, and C Chart, you assume the process produces data from a population that follows a Poisson distribution. The mean and variance of this distribution are both denoted by m. If m is not specified, Minitab estimates it from the data. Alternatively, you can enter a known process mean, an estimate obtained from past data, or a goal.

1    In the control chart dialog box, click control chart Options.

2    In Mean, enter the historical means as constants.

3    Click OK in each dialog box.

You can enter historical data in several ways:

·    A single value, which applies to all variables and stages.

·    A list of values, one for each variable. All stages for each variable use the same value.  

·    A list of values, one for each stage within each variable. Each stage for each variable uses a different value.