Little's Law is the foundation of Lean and Lean Six Sigma methodology, where Variation (Y=f(x)) of the process is also a key measure. Little's law is the Process Lead Time (PLT) = Work in Process (WIP) divided by the Exit Rate (Throughput). For example: There are 5 customers standing in line at the checkout counter and every minute 1 person completes a checkout and exits the line. PLT = 5 (WIP)/1 person every 1 minute, therefore PLT = 5 minutes. This means that the 5th person in line will wait on average 5 minutes to complete checkout. Little's Law is important because it shows us that if i can manage the workflow of my process WIP, i can predict my Process Lead Time, that as my WIP goes up, my PLT also goes up, and as my WIP goes down, my PLT goes down.
What are others' experience in establishing a WIP Cap for a predictable PLT flow? How about a work control system across the supply chain?