Calibration, Verification and Adjustment: Not the Same Thing

These three words are used interchangeably on factory floors and in purchase orders. That causes wrong quotations, wrong expectations, and audit findings.

Calibration Verification Adjustment

Question answered | How far off is it, and how sure | Does it meet the | Can we bring it closer to | are we? | requirement? | correct?

Output | Errors and uncertainties | Conforms or does not | A changed instrument | conform

Changes the instrument? No No Yes

Needs a stated | No | Yes | Usually
requirement?

• Calibration compares the instrument with a reference and quantifies error and uncertainty (VIM 2.39).
• Verification provides objective evidence that the instrument meets specified requirements (VIM 2.44). It compares the calibration result with your tolerance.
• Adjustment changes the instrument so its indications come closer to the reference (VIM 3.11). After adjustment, a new calibration is needed.

ISO 10012 combines these steps into metrological confirmation: calibrate, verify against requirements, adjust or repair if needed, recalibrate, then label.

And intermediate checks?

Intermediate checks, such as a daily check of a balance with a single weight, are not calibration. They confirm that the instrument has not changed since its last calibration. ISO/IEC 17025 (clause 6.4.10) expects them where needed to maintain confidence. They are quick and cheap, and they are often what catches a problem months before the next calibration.

A balance example

• Daily: an intermediate check with one weight near the usual load, done by the user.
• Annually, or as set: an accredited calibration covering repeatability, eccentricity and errors of indication across the range, with uncertainty (OIML R76, and EURAMET cg-18).
• If the calibration shows a large error: adjustment with the internal or external weight, followed by recalibration and an as-left result.