During this time, industrial engineering matured and then found application in many areas such as military planning and logistics for both the First and Second World Wars and manufacturing systems.
After mitigation steps are put in place, the impact of any residual variability can be addressed by allocating buffers at select points in the project production system – a combination of capacity, inventory and time.
The practice is based upon defining and controlling production systems, which typically consist of a series of inputs, transformational activities, inventory and outputs.
A set of key results used to analyze and optimize the work in projects were originally articulated by Philip Morse, considered the father of operations research in the U.S. and summarized in his seminal volume.
[8] In introducing its framework for manufacturing management, Factory Physics summarizes these results: There are key mathematical models that describe the relationships between buffers and variability.
Little's law[11] – named after academic John Little – describes the relationship between throughput, cycle time and work-in-process (WIP) or inventory.