The Partial Calibration Evidence
You are reviewing a production line after a sensor calibration audit. Twelve of 100 pressure sensors show drift beyond the manufacturer's tolerance; the drift is small (0.4–0.9%) but in the same direction. The line has run 26 days since the last calibration. Records for 8 of the 12 sensors are missing the technician's sign-off. The line produces a component with a 1.2x design safety factor; a 0.9% pressure under-read would reduce that to about 1.19x, still above the 1.0 design minimum but below the site's 1.15 operating margin. The production manager says stopping costs $180k/day and the customer penalty starts in 4 days. You have authority to stop the line or to require additional controls, but not to waive the operating margin.
1. Decide whether to stop, continue with controls, or continue unchanged. Justify against the margin and the record gaps.
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Decision: Continue for up to 24 hours under interim controls, not because the record gap is acceptable, but because the calculated worst case still clears the operating margin. Stop if the next verification fails.
Reasoning:
- Worst observed drift is 0.9% in one direction. A 1.2 safety factor under a 0.9% under-read becomes approximately 1.2 × 0.991 = 1.189, which remains above the 1.15 operating margin, though the margin is thin.
- The eight missing sign-offs mean the records are unverified, not necessarily wrong. Treat them as unverified and recalibrate those sensors before the next shift.
- The production manager's $180k/day and four-day penalty are real costs, but they do not change the margin calculation.
Interim controls: recalibrate all 12 sensors within 24 hours; increase inspection frequency on the affected line; trend pressure readings each shift; require a second person to verify sign-off. Stop triggers: any drift above 1.0%, drift reversing direction, a second sensor failing after recalibration, or failure to complete recalibration within 24 hours.
2. What would you document, and what would you refuse to sign?
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Document: the 12 drift values, the 1.189 worst-case calculation, the 1.15 margin comparison, the missing sign-off list, the interim control plan, the 24-hour expiry, the stop triggers, and who approved conditional continuation. Record that the decision is conditional and time-bound, not a waiver.
Refuse to sign:
- A retrospective calibration record for the eight sensors without technician sign-off.
- Any document that says the operating margin was met for the full 26-day run when the drift evidence does not support that.
- A blanket waiver of the margin or a permanent continuation approval.
Why: signing a record I cannot verify would convert an evidence gap into false assurance. Conditional continuation is defensible; falsified completeness is not.