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A Modified S Chart for the Process Variance

Summary: [This abstract is based on the author's abstract.]When monitoring process dispersion, quality control practitioners favor the R chart for small sample sizes. The S chart is the preferred choice for larger sample sizes because it is slightly more effective. Computers and scientific calculators have now simplified the computation of the standard deviation for each sample. Shortcomings of the standard S chart are examined, and a modified S chart is proposed to overcome these problems.

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  • Topics:
  • Keywords: Dispersion,In-control process,Out-of-control process,R chart (range chart),S chart (sample standard deviation),Type I error,X-bar control charts,Control limits
  • Author: Khoo, Michael B.C.
  • Journal: Quality Engineering