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.
Words to know: BOM, Gross requirement.
Define the planning boundary
A bottle is the parent item. Its body, cap assembly, and label are child items. A quantity on a BOM has a denominator: two seals per cap assembly is different from two seals per carton. Write that denominator beside every number. A correct multiplication using the wrong unit still gives an unusable plan.
Northstar uses one body, one cap assembly, and one label per bottle. Each cap assembly contains one shell and two seals. To make twenty four bottles from scratch, the shop needs twenty four bodies, twenty four shells, forty eight seals, and twenty four labels. Exploding the cap assembly reveals its children; it does not create another demand for finished bottles.
Calculate with explicit rules
Check whether the listed parts are stocked assemblies or instructions to build an assembly. If ten complete caps are already usable, their shells and seals have already been consumed. Subtract those caps before exploding the remaining cap builds. Otherwise the same physical requirement appears twice, once inside the stocked cap and once as new loose parts.
Versions matter because a drawing change may alter the recipe. Give each plan an effective date and a version identifier. In this exercise all bottles use version A throughout the horizon. A substitute seal is not automatically interchangeable: approval and fit must be established before its inventory can satisfy the requirement.
Check before committing
Keep a small reconciliation next to the plan. The parent quantity should explain every child quantity through a visible path. A reviewer should be able to point to a line and say which parent created it. This is more valuable than a long list of parts with no relationship to the bottle starts.
Do not attach yield loss to every level by habit. This lesson assumes perfect yield so the structural arithmetic can be checked first. Later lessons add losses at named operations. Separating structure from process assumptions makes a change easier to diagnose and avoids multiplying the same allowance twice.
- 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 | Parent starts:24 bottles; body1/bottle; cap1/bottle; label1/bottle; shell1/cap; seal2/cap. |
| 2 | Usable stock: bodies5, caps10, shells4, seals8, labels6. No receipts, scrap, or lot minimums. |
- 1. Caps to build=24−10=14.
- 2. Shell net=14−4=10; seal net=14×2−8=20.
- 3. Body net=24−5=19; label net=24−6=18.
Base net purchases:19 bodies,10 shells,20 seals,18 labels.
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. Parent starts:24 bottles; body1/bottle; cap1/bottle; label1/bottle; shell1/cap; seal2/cap. Usable stock: bodies5, caps10, shells4, seals8, labels6. No receipts, scrap, or lot minimums. 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 | Repeat for bottle starts of 18, 30, and 42 with the same opening stock each time. 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 | Stress the 24-bottle case with caps stock reduced from10 to4; separately change seals per cap from2 to3. 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 net purchases:19 bodies,10 shells,20 seals,18 labels.
- For18 starts:13 bodies,4 shells,8 seals,12 labels. For30:25,16,32,24. For42:37,28,56,36.
- With4 caps,20 cap builds need16 shells and32 seals net. With3 seals and10 caps,14 cap builds need34 seals net.
Keep these three ideas
- Convert a product recipe into component needs without mixing units.
- 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
Convert a product recipe into component needs without mixing units.
- A bottle is the parent item
- Caps to build=24−10=14.
- Base net purchases:19 bodies,10 shells,20 seals,18 labels.
First half: definitions and baseline.
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.