Start with something familiar
Two cooks may each have a stove, but they can still compete for the same mixer. A kitchen plan that checks only stove time will miss the clash. Likewise, cleaning a stove needs someone to do the work; writing two cleaning tasks at once assumes two available people. The lesson is to name every scarce item that an activity occupies. Once those names are visible, a simple timeline can reveal a conflict before the shift begins.
Words to know: No overlap, Operation, Precedence, Setup family.
One operation may occupy two resources
In this fictional cell, a setup needs both its target machine and the only technician. Running needs the machine but no technician. Therefore simultaneous runs can be fine while simultaneous setups are not. Copy each setup interval onto the technician timeline as well as the machine timeline, using the same operation identifier on both.
Avoid counting the copied setup as extra elapsed work. It is one activity with two resource requirements. A resource audit checks every resource it occupies, while the job route lists it once. This distinction helps prevent both double-counted load and hidden conflicts. State whether a person must remain for the whole run; here that is explicitly not required.
Audit intervals instead of trusting totals
Two thirty-minute setups total sixty technician minutes. That total may fit a shift even when both were assigned from zero to thirty. Capacity totals show amount, not placement. Sort intervals by resource and start time, then check that each next start is at least the previous end. Touching intervals are legal under our boundary convention.
Check precedence separately. A run cannot begin until its own setup ends, even if the machine looks free. When the technician order changes, some run starts change too. The best technician order can depend on the length of the following runs, not just the setup duration. Calculate both feasible alternatives in this small case.
Protect complete accounting
The audit list should include setup, run, downtime, and any mandatory inspection in scope. Do not add invented restrictions, but do not omit supplied ones. Mark an activity as unconstrained only when the case says sufficient capacity exists. A plan is reviewable when each exclusion is visible rather than implied by a blank cell.
The lesson deliberately keeps only two machines and one person. You can still learn the core practice: validate resources and routes before comparing outcomes. When a scenario adds an outage, preserve the original schedule as a baseline and list changed starts. A compact exception report is often easier to act on than a completely redrawn wall of work.
- Validate inputs
- Place legal work
- Check every resource
- Compare outcomes
- Release with conditions
Northstar worked schedule
All data are fictional. Time is elapsed minutes from the stated shift origin; unlisted transfer times are zero. Use the explicit resource and setup assumptions below.
| Job | Machine | Setup minutes | Run minutes | Due |
|---|---|---|---|---|
| D | M1 | 30 | 60 | 120 |
| E | M2 | 30 | 40 | 100 |
- 1. Both jobs are ready at0; one technician performs all setups.
- 2. Set up D 0-30 then E 30-60. Run D 30-90 and E 60-100.
- 3. Machines are distinct, so runs30-90 and60-100 may overlap.
D completes90 and E100 with no tardiness. Technician use is60 minutes; latest finish100.
Assumptions
- All times and quantities are deterministic inputs unless explicitly labeled expected or scenario-dependent.
- Operations cannot be split; touching interval boundaries are allowed. Additional constraints are only those stated in the lesson.
Where this can fail: These small cases teach traceable decisions, not a promise of performance in an unmodeled plant.
Build, test and explain a plan
Use the table, both machines and technician open0-240, no other setups, and non-preemptive tasks. Compare D-then-E setup order with E-then-D. Audit a deliberately invalid plan that puts both setups0-30. Then close M1 from0-40, and separately make E run80. Rebuild both orders and document changed starts relative to the original D-first plan. The eight hours are self-paced estimates for modeling, scenario work, checks, and explanation; they have not been experimentally validated.
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 lesson and make a one-page input dictionary. Define the clock, units, resource names, release rule, and all assumptions. Mark which inputs are fixed and which will change in the scenarios. |
| 0.5 | Reproduce the worked example without looking at its result, then compare every intermediate start and finish. Explain any difference in a short error log before building the larger table. |
| 3 | Build a complete operation-by-operation planning table for every requested sequence or scenario in the lab brief. Include starts, finishes, blocked intervals, due comparisons, and a resource timeline. Cross-check each row against its input and reconcile resource totals. Use paper or a spreadsheet; no special software is required. |
| 2 | Run the specified stress cases independently, restore the base between cases, and compare each changed result with the original. Create a small sensitivity table and identify which assumption caused each difference. Audit feasibility before ranking the outcomes. |
| 1 | Write a decision memo with the selected feasible option, numeric evidence, the losing option’s advantage, and any unmet promise. State the condition that would cause you to reconsider. Do not invent additional capacity or missing data. |
| 1 | Teach the result aloud or in writing to an imagined operator. Rebuild one key check from a blank page, answer the recap questions, and revise the memo if your explanation reveals an unsupported assumption. |
Your deliverables
- Input dictionary and checked schedule table.
- Scenario comparison with job-level or quantity-level evidence.
- Decision memo and teach-back record.
Check your practice work
- E setup0-30, D setup30-60 gives E run30-70 and D run60-120; final finish120, no tardiness.
- Simultaneous setups0-30 violate technician no-overlap even though machine calendars permit them.
- With M1 closed0-40, E setup0-30 then D setup40-70 gives E complete70 and D130; D tardiness10.
- With E run80, D-first gives D90,E140, total tardiness40; E-first gives E110,D120, total tardiness10.
Keep these three ideas
- Identify plans that look fast only because work or shared resources were omitted.
- Which constraint or metric changes the choice in this case?
- What assumption must be confirmed before this plan can be released?
Common mistakes
- Comparing plans before checking every stated constraint.
- Changing several assumptions at once and losing the explanation for the result.
Optional video study
Identify plans that look fast only because work or shared resources were omitted.
- Introduce the specific Northstar inputs
- 1. Both jobs are ready at0; one technician performs all setups.
- D completes90 and E100 with no tardiness. Technician use is60 minutes; latest finish100.
Second half of module narration
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.