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: Pegging, Time fence, Planned release.
Define the planning boundary
A planning exception marks a mismatch between the intended plan and current evidence. It can be a late receipt, a yield loss, an overload, or a version change. Start by identifying which assumption changed. Rebuilding every number without preserving the reason makes it hard to tell whether the revision solved the actual problem.
Northstar plans two shipments. There are ten usable bottles at the start of week one, a twenty-bottle receipt in week one, and a twenty-five-bottle receipt in week two. Demand is twenty eight and twenty four. The baseline ends week one with two and week two with three. Both due dates are covered.
Calculate with explicit rules
If ten bottles from the first receipt slip to week two, week one has only twenty against demand of twenty eight. Eight units become backlog. In week two, the delayed ten and the planned twenty five arrive. After serving eight backlog and twenty four new demand, three remain. The final balance is unchanged, but service in week one is worse.
A total-stock report may therefore miss the most important event. Report on-time units separately from eventual fulfillment. A promise about week one cannot be repaired retroactively by an abundant week-two balance. A planner should give customer-facing teams the affected quantity and credible revised timing.
Check before committing
Change control records the old value, new value, reason, approver, and timestamp. The class case asks for a written comparison rather than a software workflow. A small structured change log is enough to show that material, capacity, and shipping were reconsidered before a revised release was authorized.
Close the loop after execution. Compare actual output and receipt timing with the planning assumptions. One bad batch is not enough to rewrite a long-run yield estimate automatically, but repeated deviations deserve investigation. Separate parameter learning from emergency recovery so that a temporary fix does not become an unexplained permanent planning rule.
- 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 | Opening usable10; baseline receipts weeks1–2:[20,25];demands[28,24]. Zero safety stock;perfect yield for receipt balances. |
| 2 | Disruption moves10 units from week1 receipt to week2. Recovery can expedite8 of those delayed units back to week1 for$64. No extra total supply. |
- 1. Baseline ending balances[2,3].
- 2. Disrupted week1:20 supply−28 demand gives8 backlog,0 stock;week2:35−8−24=3 stock.
- 3. Recovery receipts[18,27];week1 stock0;week2 stock3;on-time demand52 of52.
Disruption on-time units20+24=44 of52,84.62%;8 prior units fulfilled late in week2.
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. Opening usable10; baseline receipts weeks1–2:[20,25];demands[28,24]. Zero safety stock;perfect yield for receipt balances. Disruption moves10 units from week1 receipt to week2. Recovery can expedite8 of those delayed units back to week1 for$64. No extra total supply. 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 baseline, disruption, and recovery balance tables with separate stock and backlog. 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 | Test only4 units expedited; separately increase week2 demand by6 with the full8-unit expedite. Assume no other supply and report remaining backlog. 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
- Disruption on-time units20+24=44 of52,84.62%;8 prior units fulfilled late in week2.
- Expedite4:week1 on-time24,backlog4;week2 ending3;on-time48/52=92.31%.
- Full expedite and week2 demand30 gives3 backlog at end week2 and0 stock;on-time55/58=94.83%.
Keep these three ideas
- Replan with an audit trail and explain customer consequences.
- 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
Replan with an audit trail and explain customer consequences.
- A planning exception marks a mismatch between the intended plan and current evidence
- Baseline ending balances[2,3].
- Disruption on-time units20+24=44 of52,84.62%;8 prior units fulfilled late in week2.
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.