In some process control applications it may be necessary to limit the sample size to one measurement.A possible option would be to use an individual measurement chart for moitoring the process center,and using a moving range chart for monitoring process varibility(X-MR).There has been an ongoing debate,and there are conflicting views in publications whether it is necessay to use a Shewhart moving range chart when there is no disadventage in using the X-MR procedure based on average run length values.However,there are other considerations that justify the use of the X-MR procedure over the X-chart alone.In this article chats.We limit discussions to the case where it is reasonable to assume normality and negligible autocorrelation in the data
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