Bottleneck flow across the route

Understand the constraint

In the simplified Northstar route, the supplier supports twenty four good bottles, manufacturing supports thirty two, and shipping supports thirty. All three figures refer to the same week and the same finished good equivalent. The maximum new completed flow is the smallest of the three, twenty four. The net requirement is twenty nine, so the route leaves a five bottle shortfall. These capacities are good-unit ceilings for this example; do not apply the ninety seven percent yield factor again to them.

Local spare capacity is useful only if it can help the constrained route. Adding four manufacturing units changes its ceiling to thirty six but leaves the route at twenty four. Adding five supplier units raises the supplier limit to twenty nine, enough for the stated requirement. Adding ten supplier units makes shipping, at thirty, the next limit. The identity of a bottleneck can therefore change as recovery actions change the feasible set. Always recalculate the whole route after each action.

Interpret the result

The minimum rule assumes one product, a common time window, compatible units, no usable intermediate stock, and stages that can pass the required flow on time. If a pallet waits between stages or a truck leaves before production ends, the weekly minimum is only an upper bound. Flow conservation also matters: upstream releases should not be mistaken for customer shipments. Label starts, good production, packed bottles, and shipped bottles separately. This helps reveal where work is waiting and where a promise can actually be made.

Create one row for each resource or stock position and one column for each time bucket. Put the unit in the row label and keep inputs separate from calculated results. Begin with the smallest case you can verify by hand, then extend the same equations across periods. Give every receipt a usable date and every requirement a due date. Preserve the baseline before changing an assumption so the effect of an action is visible.

Validate and explain

Use a second check that follows the physical story. Count what enters, what is used, what waits, and what leaves. A plan that balances in total can still fail at an earlier cutoff. Mark any unavailable input as an assumption rather than filling it with a convenient zero. A zero means a known absence; an unknown value means the promise remains conditional. This difference belongs in both the model and the decision note.

A calculation becomes useful when it changes a choice. Compare the baseline with at least two scenarios, identify the first limiting condition in each, and explain what additional resource would actually change delivered output. Keep a service measure alongside any cost or value measure. State whether the choice maximizes value, protects a commitment, or reduces the worst shortfall. A different goal can produce a different sensible answer from the same facts. Finish by testing one deliberately wrong proposal, such as a receipt used before arrival or a quantity above a resource ceiling. Your table should make that error visible. Save the rejected proposal with a short explanation, because it teaches a reviewer how the checks work. The eight hours include rebuilding, scenario work, writing, and teach-back; they are self-paced estimates rather than measured completion times. Faster readers should deepen the checks instead of merely rereading the text.

Build, test and explain a plan

Construct a four-week route table. Net needs are 29/28/31/27. Supplier limits are 24/30/28/29, manufacturing 32/26/34/30, and shipping 30/30/29/26. No inventory carries between weeks. Test four extra supplier units in each week, then four extra manufacturing units, and identify when either action creates no shipment gain. The eight-hour estimate covers an original workbook or paper model, scenario calculations, checks, and communication; it is not experimentally validated.

Use paper or a spreadsheet. The estimates below include the study and worked example already on this page.

Your deliverables

• A reproducible planning table with inputs, formulas, units, and checks.
• A scenario comparison with service and resource consequences.
• A decision memo and short teach-back outline.

Keep these three ideas

• Find the limit on completed flow rather than celebrating local speed.
• Keep quantities, resource units, and due times explicit.
• Recheck all constraints after a change, and report remaining uncertainty.

Common mistakes

• Treating capacity in a later time bucket as available before the due gate.
• Calling an expected or conditional quantity a guaranteed shipment.