Following Duncan [3], the per hour cost of the process under the surveillance of a mean chort for controlling the mean of non-normal variables whose density function is represented by the first four terms of an Edgeworth series is obtoined. The sample size and sompling interval which minimize the cost for detecting a particular shift in the process average are derived when the width of the control limits is specified. They are numerically determined for different non-normol situations by assuming various cost valuer when a particular shift in the process averoge is to be detected. They are presented in a fable which compares the changes in optimum sample size and sompling interval due to changes in [ a ) the non-normal sifuotion, (b) the shifts to be detected in the process averoge and (c) width of the control limits specified.
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