Verdict
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Control limits come from the process's own variation, not the tolerance: a process can sit inside spec while drifting badly, and a chart drawn against the specification never shows it. Capability is withheld while the process is out of control - Cpk on an unstable process describes a process that no longer exists.
Individuals chart
reading centre line control limits (±3σ) specification limits rule fired
Rules that fired
| Rule | Where | What it means |
|---|