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The Rules of OPT - precursor to Theory of Constraints

the only rule is workI have heard a number of references to the "Rules of OPT" by people in the Theory of Constraints community.  I have known that OPT was the software that Eli Goldratt developed and sold for shop floor management before he developed what became Theory of Constraints and its Five Focusing Steps.  The Rules of OPT are a familiar set of guidelines and principles, rather than a process to follow.

The Rules of OPT.  I have seen and heard most of these through my education in Theory of Constraints.  I just didn't know they came from the OPT world. 

  1. Utilization and activation of a resource are not the same.
    • Essentially, just being active is not the same as being useful and effective to the overall system.  Many organizations just measure the activity of their resources, not the effectiveness (utilization) of their resources.
  2. The level of utilization of a non-bottleneck is determined not by its own potential but by some other constraint in the system.
    • Any non-bottleneck should be "utilized" such that the bottleneck is never starved for work and all work that is processed by the bottleneck is high quality.  Otherwise, additional activation of these resources just generates excess work-in-process.
  3. An hour lost at a bottleneck is an hour lost for the total system.
  4. An hour saved at a non-bottleneck is just a mirage.
    • This is a classic pair of statements, usually uttered at the same time.  If you save time on a resource that has excess capacity, you haven't really saved that time.  But if you save time at the bottleneck - the resource that is limiting the flow through your entire system - then you are golden!
  5. Bottlenecks govern both the throughput and inventory in the system.
  6. The transfer batch may not and often should not be equal to the process batch.
  7. The process batch should be variable, not fixed.
    • Batch sizing is an important discussion when it comes to deciding how to operate.  I don't always see it in discussions of the basics of Drum-Buffer-Rope and other solutions derived from TOC.
  8. Capacity and priority should be considered simultaneously, not sequentially.
  9. Balance flow, not capacity.
  10. The sum of local optima is not equal to the global optimum.

Note the use of "bottleneck" throughout, rather than "constraint."  This reflects the early days - and often the continuing view that people have of Theory of Constraints.  (I still use bottleneck to refer to temporary bottlenecks in the system while we strive to reach a strategic constraint or control point.)

I found this particular wording and order in this presentation on OPT from the Richard Lee Storch's Industrial Engineering 337 course at the University of Washington.  I've also seen it as nine rules instead of ten, such as Rules for bottleneck scheduling in TOC.

[Photo: "the only rule is work" by caren litherland]

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