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Principle (Best Case Performance): The maximum throughput and minimum flow time for a line with a given bottleneck rate and raw process time as a function of WIP level are given by the following figures.
 
 

Relationship between Throughput and WIP for Best Case

Relationship between Flow Time and WIP for Best Case

Note that flow time remains constant up to a certain WIP level; after which it starts rising linearly with WIP. Similarly throughput rises linearly for low WIP, but then levels off at the bottleneck rate beyond a certain WIP level. This WIP level at which is the critical WIP, which we note is the only WIP level for which flow time is minimized and throughput is maximized.

The best case occurs (click here for derivation) when:

• there is absolutely no variability (i.e., no failures, yield loss, rework, etc.) and,
• all jobs are processed and moved one-at-a-time (i.e., so that there is no time wasted waiting to form and unform batches).

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