Modify Model 12-4 from Section 12.5.2 to terminate the replication when the ratio of the half width to the midpoint (point estimate) of the automatic batch-means run-time conf dence interval on steady-state expected total WIP falls below 0.04; that is, when the relative precision is 4%. The Arena variable DAVG(Dstat ID) returns the current average of the indicated Dstat (that is, time-persistent) statistic. Note that the condition you want to check is of the form H / A , 0.04, where H is the half width and A is the point estimate, which can be an uncomfortable calculation if A 5 0 (which it will be at the start of your run). Instead, check the condition in its equivalent form, H , 0.04 A .