A computer simulation of an assembly line enforcing pacing on manned sequential stations indicates that unpaced station operations are superior to paced. Using the variability and work-time distribution of operator performance on repetitive tasks, a number of studies were carried out which show that an assembly line cannot perform at maximum efficiency (in terms of operator idle time and units completed) unless queues are provided before each work station. Studies of various station speed configurations indicate that the generally preferred configuration is Fast-Medium-Slow (short-medium-long cycle time) and that there is little difference among various configurations when the inter-arrival time is larger than any of the operator mean cycle times.