Control Charts

The Control Charts are described in the AIAG manual, although Mesa generates the actual charts in a different way.  Mesa generates the charts in an overlapping format, while the AIAG manual separates them.  The overlapping format is particularly useful where relatively large numbers of operators (or equivalent) are being studied.  The Control Charts generated by the AIAG example data set are shown below, with the first chart being a plot of the test-retest ranges for each part by each operator:



In the AIAG manual the upper chart is called the Repeatability Range Control Chart and each operator plot is shown individually (see page 62 of the 2nd edition).  This chart indicates whether or not the measurement process is being used consistently.  A point outside the upper limit on the Range chart is evidence that the measurement process is NOT being used consistently. The second control chart generated by Mesa is the chart of means for each part by each operator:

In the AIAG manual the lower chart is called the Part Appraiser Average Chart (see page 63 of the 2nd edition).  The chart of means shows the observed part to part variation along with the 'noise band' due to measurement error (i.e. test-retest).  The more points outside the limits on the Means Chart, the better the discrimination of the measurement process.