I've been collecting defect data for quite a while. PPM measurement
was the first thing I binned and started up SPC charts, namely
multi-characteristic u-charts. This way you show exactly what defects
you are measuring and if your overall manufacturing process is in
control. Few folk, if any, have questioned our defect tally since
these charts were introduced.

Martin Farrell (Chemist/ Quality Engineer)
Marconi Electronic Systems,
Edinburgh.

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