It is widely known that lead-time and utilization are dependent on work in pro-gress (WIP). This article validates the functional relationship between inventory deviation and lead-time by means of simulation. In addition, the results confirm a new mathematical model for the logistic operating curves in practice. A new ap-proach is based on the idea that changing a machine from overload to under-load and vice versa results in a waste of utilization and therefore in an increase in lead-times. The frequency of the changes from under- to overload and vice versa which determines this waste, is measurable by means of the statistical deviation of the inventory.