Start with something familiar
Imagine planning a meal for a group of friends. You need to know who is coming, what each dish uses, which food is already usable, and when the oven is free. A full pantry does not help if the missing ingredient arrives after dinner. Nor does a long recipe prove that you can cook it before guests arrive. Manufacturing planning applies that same care to parts, unfinished work, available time, and the promises made to customers.
Define the planning boundary
Work in process has passed some operations but is not yet available to ship. Its value in a plan depends on what remains, when that work can finish, and which inspections it must pass. Ten partly assembled bottles do not automatically equal ten usable bottles due tomorrow.
Northstar records eight units after assembly and before final inspection. The remaining expected yield is ninety five percent, so expected good supply from that group is seven point six. Do not apply the earlier assembly loss again. The units already survived that stage, and their status is part of the starting information.
Calculate with explicit rules
Expected supply can be fractional, but a firm shipping promise is expressed in whole accepted bottles. For this planning exercise, use expected WIP output in the model and round only the new starts upward. The answer key shows the arithmetic. The decision memo must separately discuss uncertainty and avoid claiming that seven point six bottles can physically ship.
WIP can also be late. If final inspection happens after the demand cutoff, exclude that batch from timely coverage even if it is almost complete. A small remaining operation is not proof of a short queue. A planner needs the resource slot and an agreed completion time, not only a percentage-complete estimate.
Check before committing
Reconciliation prevents double counting. If a WIP order appears as a scheduled finished receipt, do not add its stage quantity again as another supply. Use one representation of that order in the balance. Retain its identifier so a reviewer can trace the receipt to the physical batch and its remaining work.
A sensible control separates expected planning output from confirmed accepted output. The first helps reserve time and parts; the second authorizes shipment. As inspection results arrive, replace the expectation with actual good quantity and recalculate the residual need. Never keep both the old estimate and the new actual quantity in the same supply total.
- Read case inputs
- Calculate the baseline
- Change one assumption
- Check and decide
Northstar worked case
All data below are fictional and complete for this calculation.
| Input group | Exact case data |
|---|---|
| 1 | Good requirement29 after stock and other receipts; WIP8 due before cutoff; remaining WIP yield95%. |
| 2 | New starts yield97%,whole units; WIP is not included in any other receipt. |
- 1. Expected WIP good=8×0.95=7.6.
- 2. Residual expected target=29−7.6=21.4.
- 3. New starts=ceil(21.4/0.97)=23; combined expected good=29.91.
Base new starts[30,23,19,11]; combined expected output[29.1,29.91,29.83,29.67].
Assumptions
- Only the stated supply and demand exist; no hidden safety stock or open orders.
- Timing, yield, lot size, and setup follow the explicit case; do not import another lesson’s assumptions.
Where this can fail: This deliberately small model checks planning logic. It cannot establish supplier reliability, customer priority, or a statistical service guarantee.
Build, test and explain a plan
Northstar asks you to build a reusable planning model, not just report one answer. Use only the inputs below and the worked example. Good requirement29 after stock and other receipts; WIP8 due before cutoff; remaining WIP yield95%. New starts yield97%,whole units; WIP is not included in any other receipt. Keep full precision in intermediate calculations and round only where the case requires whole units. Use separate tabs or clearly labeled paper grids for the baseline and each scenario. The eight hours are a self-paced practice estimate, not an experimentally validated duration.
Use paper or a spreadsheet. The estimates below include the study and worked example already on this page.
| Estimated hours | Activity |
|---|---|
| 0.5 | Study the terms and mark each input with its unit, date, and status. Write a half-page statement of the boundary of the model and list facts that are deliberately excluded. |
| 0.5 | Recalculate every worked-example step by hand. Compare the hand calculation with your model and explain any difference before moving on. |
| 3 | Build four cases with WIP[0,8,12,20], remaining yield95%, good requirement29, and new-start yield97%. Build formulas, a visible input table, and a reconciliation row. Add notes so another learner can reproduce the model without asking you for missing data. |
| 2 | Make all WIP late; separately replace expected WIP with confirmed accepted output[0,7,10,18]. Save each scenario separately. Compare quantities, dates, and any unresolved shortages. Trace the change from its input through every affected calculation. |
| 1 | Write a one-page decision memo naming the baseline result, the preferred action under each scenario, the remaining uncertainty, and the evidence required before execution. Do not invent costs or customer priorities. |
| 1 | Create a five-minute teach-back with one diagram and one checked number. Then use a second independent calculation to audit the model and revise unclear assumptions. |
Your deliverables
- An auditable input and calculation table with baseline and scenario tabs.
- A comparison table with numerical checks, dates, and unresolved gaps.
- A decision memo and a short teach-back using the supplied facts.
Check your practice work
- Base new starts[30,23,19,11]; combined expected output[29.1,29.91,29.83,29.67].
- Late WIP means30 new starts in each case.
- Confirmed accepted outputs yield new starts[30,23,20,12]; no remaining WIP yield is applied to accepted output.
Keep these three ideas
- Assess unfinished supply by stage, timing, and remaining loss.
- A numerical answer must retain its unit, timing, and assumptions.
- Use the scenario checks to test the model before using it to support a decision.
Common mistakes
- Combining values that refer to different dates or different physical units.
- Treating a modeled proposal or expected output as confirmed usable supply.
Optional video study
Assess unfinished supply by stage, timing, and remaining loss.
- Work in process has passed some operations but is not yet available to ship
- Expected WIP good=8×0.95=7.6.
- Base new starts[30,23,19,11]; combined expected output[29.1,29.91,29.83,29.67].
Second half: scenario comparison and decision.
Open the module media & quizPut this idea to use
Carry your assumptions into a practical tool, then compare your result with a short guide.
Open a related planning toolRead the related planning guidePractice with the planning gameThis saves a completion marker in this browser only. It does not verify time spent.