4.5.7 Estimating the Utilization of S/R Machines The performance evaluation of an automated storage and retrieval system is based on the percentage utilization of S/R machines. Suppose there are N number of S/R machines in the system and each aisle is served by one S/R machine. Then the number of transaction per S/R machine per hour is Nt=NST where ST is the system throughput for an AS/RS. System throughput depends on the relative numbers of single and dual command cycles performed by the system. Let be the number of single command cycles performed per hour, and be the number of dual command cycles per hour, at a specified or assumed utilization level. Then an equation can be formulated for the amount of time spent in performing single command and dual command cycles each hour and is given as : Tsc+Tdc