Workload norms are deterministic parameters setting a maximum, a minimum or a reference workload level, accordingly to the workload control strategy used, on each capacity group. To determine the best performing workload norms levels ,it is a common practice in simulation studies (e.g. Thurer et al., 2010; Henrich et al., 2007; Land, 2006; Oosterman et al., 2000) to define it as an experimental variable. Experimentation was started with a large value for assuring that the release of orders to the shop floor was not constrained by load limits. In such a situation, immediate release takes place. Then, workload norm levels were stepped down, in order to gradually increase the level of restriction to the release of orders i.e. from unrestricted to highly restrictive values. Since machines exhibit identical characteristics, i.e. utilization, operation processing times and stream of arriving orders and average flow times, norm values were set identical for all capacity groups. Only when work centre 1 is split in two capacity groups, different workload norm values have to be set. In this study, they are related by a fixed percentage to the norm values of the other capacity groups. This percentage was determined through some pilot simulation runs, under an immediate release.