This paper describes a novel method of calculating the sensitivity of the manufacturing system throughput to the variables of the machines. The sensitivity analysis needs only a single simulation, yet is easy to use and provides accurate results. This sensitivity analysis is then used to predict the change in the system throughput due to a change of the variables of the ma-chines provided that the system change does not significantly change the bottleneck. These predictions can be used for a local optimization, allowing the use of a steepest descent optimization algorithm. The method is based on improving the momentary shifting bottlenecks. The shifting bottlenecks are detected using the shifting bottleneck detection method based on the active duration, i.e., the time a machine is active without interruption. The method is easy to understand and easy to implement in existing simulation software.