I studied queueing theory at school 20 years ago for my CompSci degree. Last year I implemented a QT model (relatively simple version of M/M/1) to control the q

I studied queueing theory at school 20 years ago for my CompSci degree. Last year I implemented a QT model (relatively simple version of M/M/1) to control the queueing length at a very large chain of hypermarkets (core mechanism: use historic lambda and mu timeseries to predict future lambda and mu, reverse engineer the formula to get the right number of checkout counters to keep average queueing length to the desired number of seconds). The thing is now used across many countries. Very satisfying payoff after 20 years..