Statistical process control, SPC
In a control diagram, the results of sampling at more or less regular intervals from a process of some kind are plotted. Often plots are made of both the mean value as well as some measure of scatter for the sampling tests, for example, variation width or standard deviation. In the diagram one also normally draws limits within which the results should lie if the process is behaving “normally”(under statistical control). Control diagrams have been developed originally in the monitoring of manufacturing processes but the technique is even applicable to measurement processes. The results for unknown test objects cannot however be used since they have different and unknown true values. One measures instead one or more special test objects (control objects).
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ISO CD11462  


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