Operations Management: Processes and Supply Chains, 12th Edition

Key Equations

Performance Measures for Scheduling Processes

1. Performance measures:

   $$\begin{array}{ccc}\hfill \text{Flow time}& =& \text{Finish time }+\text{ Time since the job arrived at the workstation}\hfill \\ \hfill \text{Past due}& =& \text{Time by which a job missed its due date}\hfill \\ \hfill \text{Makespan}& =& \text{Time of completion of last job }–\text{ Starting time of the first job}\hfill \\ \hfill \text{Total inventory}& =& \text{Scheduled receipts for all items }+\text{ On-hand inventories of all items}\hfill \end{array}$$

Job Shop Scheduling

2. Critical ratio:

   $$\text{CR}=\frac{\text{Due date}-\text{Today'}\text{s}\text{d}\text{a}\text{t}\text{e}}{\text{Total shop time remaining}}$$

3. Slack per remaining operations:

   $$\text{S}/\text{RO}=\frac{\left(\text{Due date}-\text{Today'}\text{s}\text{d}\text{a}\text{t}\text{e}\right)-\text{Total shop time remaining}}{\text{Number of operations remaining}}$$