This is a model of a simple business process in a billing department. Invoices of two types arrive at the department: normal and special - those that have special contracts as to how they should be billed. At random, some of the accounts are audited by a supervisor. All bills are printed on the same printer, and are stuffed and mailed in the same way. You can see the animation of the process, the distribution of the bill processing times, and play with the bill arrival rates and resource capacities on-the-fly.