A synthetic control chart for monitoring the changes in the standard deviation of a normally distributed process is proposed in this paper. The synthetic chart consists of the sample range (R) chart and the conforming run-length (CRL) chart. The R chart can be viewed as a special case of the synthetic chart. The operation, design and performance of this chart are described. Average run-length comparisons between other procedures and the synthetic chart are presented. It indicates that the synthetic chart is a good alternative for monitoring process dispersion. The variable sampling interval (VSI) schemes, as an enhancement to the synthetic chart, are discussed to further improve the chart performance. An example is presented to illustrate the application of synthetic chart and its VSI scheme.Keywords Control chart · Conforming run length · Process dispersion · Variable sampling interval Nomenclature n sample size R sample range W relative range CRL conforming run length k + coefficient of upper control limit of the R chart for δ > 1 k − coefficient of lower control limit of the R chart for δ < 1 L lower control limit of the CRL chart δ magnitude of the change in the process standard deviation δ d magnitude of the change in the process standard deviation that should be detected as soon as possible F(·) cumulative distribution function of W ARL R average number of R samples required to detect for the R chart
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.