hardScenarioCase StudySeniorStaffLead
A customer returns three failed units built in different weeks. You have one shift to say what else is affected. How do you bound it?
6 min readUpdated 2026-08-15
Answer
Short answer
Intersect the lineage of the three units to find what they share, then forward-trace from every shared factor you cannot yet exclude. Containment starts as the union of those populations, because narrowing later is cheap and widening later is the thing that destroys credibility.
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Likely follow-ups
- Cavity number was never recorded. What is the smallest population you can honestly claim?
- Two of the three units passed through a subcontracted operation. What does that do to the boundary?
- How do you treat units that were reworked and re-serialised?
- What would you change in the data model on Monday so the next escape is narrower?
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