Imagine you are the owner/operator of a custom printing business. One morning you arrive at work and discover you have five customer orders that have different requirements and different total processing times

You ponder the sequence for a while and then decide to run the printing jobs in first-come, first-served order. What are some measures you could apply to your performance to measure whether you have done a good job? How is each measure calculated?

The two measures discussed in the text are flow time and past due. These values can be calculated for each customer order and then an overall average flow time and average past due can be calculated for the FIFO sequence. Flow time is the finish time added to the time since the job arrived. Since the five customer orders are ready when you arrive that morning, then each job's flow time will be the job's finish time. The past due measurement is the amount of time by which the job has missed its due date. In this example, the value Due Time — Completion Time = Past Due. Again, these values can be calculated for each job and these values can then be averaged for an overall average past due measure.