It is commonly believed, that improving the machine or AGV with the largest utilization improves the throughput. Unfortunately, this is not always the case, as the utilization is a rather imprecise measure of the bottleneck. This paper presents an AGV system, where improving the machine with the largest utilization does not improve the overall system. Rather, the AGV’s with a smaller overall utilization are the bottleneck. The paper applies a bottleneck detection method based on the active periods of the machines and AGV’s, which is able to detect the bottlenecks reliable and accurate.