What “Out of Tolerance” Really Means in Regulated Calibration (and Why It Triggers Reverse Traceability)
Executive Summary
In regulated industries, an Out-of-Tolerance (OOT) condition isn’t just a failed calibration — it triggers a quality system response. Once a device is found not fit for its intended use, ISO 9001 and AS9100 require companies to look backward and revalidate prior measurements. That look-back process, known as reverse traceability, is where most of the time, cost, and compliance exposure comes from.
The Real Issue Isn’t the Failure — It’s What Came Before It
Most teams think the risk lies in the failed measurement. In reality, the tolerance miss is just the moment the system caught the issue. Regulators care about everything that happened before the failure was detected.
Tray Eason explains this clearly: if a device is found unfit for its intended purpose, all prior measurements that relied on it must be reassessed.
That triggers investigation, documentation, and—when needed—rework or justification.
Why ISO 9001 and AS9100 Treat OOT as a Quality System Event
Under ISO 9001 and AS9100, measurement devices aren’t just “tools” — they are controls that validate conformity. If that control is questionable, the conformity decision becomes questionable as well.
That means:
- The OOT event is regulatory, not technical.
- The burden shifts from calibration → quality.
- Reverse traceability becomes mandatory.
You are no longer proving the device failed — you are proving the product is still good.
Why “Fit for Intended Use” Is the Actual Compliance Question
One of the most misunderstood parts of OOT investigations is that passing/failing a manufacturer spec is not the point. The question is whether the device was still adequate for how you actually used it.
Two identical OOTs can mean very different things:
| Situation | Regulatory Risk |
| Drift occurred in a range you never used | Typically low |
| Drift affected the exact range used in production | Potentially high |
This is why OOTs require evaluation, not just documentation.
A Simple OOT Response Checklist
When a device fails, quality teams can streamline investigation by following a structured approach:
- Identify the device and failure mode
- Determine last known good calibration date
- Review where and how the device was used
- Compare drift to actual process tolerance
- Document the risk conclusion and justification
If Step 4 is skipped, teams often overreact—or worse—fail to justify their decision during audit.
The Cost of OOTs Comes From Time, Not the Calibration
Most of the burden created by OOTs is internal:
- time spent searching past usage,
- documentation reviews,
- quality approvals,
- rework and recalls when necessary,
- and sometimes CAPA overhead.
NOTE: Even when the final conclusion is “no impact,” the work is still required as the cost of “no impact” OOTs comes from time, not the calibration.
Companies that have not prepared for this step experience the highest disruption.
CTA: Learn How to Reduce the Burden Before It Happens
This short guide is part of a broader OOT readiness series. If your team wants to reduce investigation time and compliance exposure:
- Watch SIMCO’s OOT Webinar Playlist – a deeper dive into how OOT investigations actually work in practice.
- If your calibration program is creating preventable OOTs, you can also request a consultation or quote to identify interval alignment and prevention strategies.