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Industrial Statistics with Minitab by Xavier Tort-Martorell Llabres, Lluis Marco Almagro, Pere Grima Cintas

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18.4 I Chart Options

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Parameters

Allows entering the mean and standard deviation of the process and Minitab calculates the limits with both values. By default, these parameters are estimated from the data.

Estimate

It allows you to skip samples (subgroups) from the calculation of the limits. This is useful when you have the certainty of the presence of special causes in a sample.

S Limits

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Tests

By default, only the symptom of special cause for one point beyond the limits (pattern 1) is activated. There are eight symptoms available and it is possible to activate the ones of interest by this option.

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In our case, if all options are activated two more points appear marked with pattern 5 (two out of three beyond two sigmas) and pattern 7 (15 consecutive points within one standard deviation from the mean).

Activating all alarm signs increases the risk of false alarms.

Stages

Mark groups on the graph. We go back and change variable ‘pH F’ (Friday's pH value) by ‘pH’ (all days' ...

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