SC QUALITY GUILDCalibration recall and out-of-tolerance impact
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Track calibration due dates for a gauge list, flag out-of-tolerance as-found results, and work out which lots measured with a bad gauge may contain nonconforming product.
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What a recall system has to do
A calibration recall system makes sure every measuring instrument comes back for calibration before its interval runs out. Each instrument needs a unique ID, a stated interval, the date of its last calibration and a due date that users can see on the gauge itself. An instrument past its due date is treated as out of calibration and is pulled from use, even if it would have passed.
As-found and as-left
The calibration record carries two results. The as-found reading is taken before any adjustment and tells you whether the instrument was right while it was in use. The as-left reading is taken after adjustment and only tells you about the future. An as-found error beyond the instrument's tolerance is an out-of-tolerance (OOT) condition, and it is the result that drives action on product.
The impact assessment
ISO 9001:2015 clause 7.1.5.2 requires the organization to determine whether the validity of previous measurement results was adversely affected when equipment is found unfit, and to act as needed. In practice:
- Set the suspect window: from the last calibration where the gauge was found in tolerance to the date it was found OOT.
- List every lot accepted with that gauge in the window, with the recorded readings.
- Remove the as-found error from each reading (true value is about the reading minus the error) and compare with the product limits.
- Readings that move outside the limits mark lots that may contain nonconforming product. Contain them, re-inspect with a good gauge and notify customers of anything shipped.
The correction assumes the error was present for the whole window. That is the conservative assumption, since you rarely know when the drift began.
Common traps
- Recording only the as-left result, which hides the OOT condition.
- Confusing the instrument tolerance with the product tolerance. The first decides OOT; the second decides whether product is affected.
- Getting the sign wrong. A gauge that reads high makes parts look bigger, so parts near the lower limit are the ones at risk.
- Treating calibration as proof of a capable measurement. Calibration checks accuracy against a traceable standard; it says nothing about repeatability or reproducibility.