All production systems are constrained by a bottleneck. Improving the bottleneck machine improves the whole production system. In addition, the bottleneck is usually not static but changes between different machines, creating one main bottleneck and a number of less important secondary bottlenecks. The presented method is able to detect and monitor the shifting bottleneck and to detect the main and secondary bottlenecks. Additionally, the accuracy of the results can be measured using only one simulation, allowing the automatic termination of a simulation after reaching a required precision.