A classical method of measunng the number of lobs m a trine-shared computer system ,s to collect statistics at the epochs of quantum completions.A computer system utilizing round-robin quantum allocations ~s modeled as a feedback queue with Poisson amvals and exponential service times, and the bias in the stausuc taken at the quantum compleuons is quant,fied.The difference botween this statistic and the true Ume-average system size is given for such a system including quanta and overhead.