Calibration Fundamentals · 5 min read
As-Found / As-Left Data — and Why You Should Demand It
If you take one habit away from this whole cluster, make it this: ask for as-found data. It is the difference between a calibration program that can answer “was our product affected?” and one that can only shrug.
Part of our guide to Calibration Fundamentals: What It Is and Why It Matters.
The two snapshots
As-found data records the instrument’s performance when it arrived at the lab, before any adjustment. As-left data records it after adjustment or repair. Together they tell a story: here is how the instrument was actually behaving while it measured your parts, and here is how it behaves now.
Why it matters more than the sticker
When an instrument comes back out of tolerance, most quality systems (and standards like AS9100 and ISO 13485) require you to assess whether measurements made with it were valid — and to act on any nonconforming product. You cannot do that assessment without knowing how far out of tolerance it was, which is exactly the as-found data. A “PASS” with no numbers leaves you guessing, or worse, unable to prove anything either way.
Common questions
Do I always need as-found data?
For instruments that verify product conformity in a regulated quality system, effectively yes — it is what supports an out-of-tolerance impact assessment. For low-stakes shop tools, a simpler certificate may be acceptable. Match the certificate to the risk.