Chapter 5 Little's Law
John D.C. Little and Stephen C. Graves Massachusetts Institute of Technology

The average waiting time and the average number of items waiting for..a service in a service system are important measurements for a manager. Little's Law relates these two metrics via the average rate of arrivals to the system. Thisfundamental law has found numerous uses in operations management and managerial decision making.

Introduction
Caroline is a wine buff and bon vivant. She likes to stop at her local wine store, Transcendental Tastings, on the way home from work. She browses the aisles looking for the latest releases from her favorite vineyards. Occasionally she picks up a few bottles. She stores these in a rack in a cool corner of her cellar. She and her partner eat out frequently but when they are at home they usually split a bottle of wine at dinner. Sometimes they have friends over and that puts a bigger ,dentin the wine inventory. They have been doing this for some time. Her wine rack holds 240 bottles. She notices that she seldom fills the rack to the top but sometimes after a good party the rack is empty. On average it seems to be about 2/3rds full, which would equate to 160 bottles. Many wines improve with age. After reading an article about this, Caroline starts to wonder how long, on average, she has been keeping her wines. She went back through a few months of wine invoices from Transcendental and estimates that she has bought, on average, about eight bottles per month. But she certainly doesn't know when she drank which bottle and so there seems to be no way she can find out, even approximately, the average age of the bottles she has been drinking. This is a good task for Little's Law.

D. Chhajed and TJ. Lowe (eds.) Building Intuition: Insights From Basic Operations Management Models and Principles. doi: 10.1007/978-0-387