Dictionary · Quality & Accreditation
Guard band
An interval applied between the tolerance limit and the acceptance limit to control the risk of false accept or false reject given measurement uncertainty — commonly the expanded uncertainty U, per ILAC-G8.
Related terms
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Check standard
A stable artifact or instrument measured regularly within a measurement assurance program; its control chart reveals drift, shifts, or loss of statistical control of the process.
NIST SOP 30 / GLP 1
Interlaboratory comparison
Organization, performance, and evaluation of measurements on the same or similar items by two or more laboratories under predetermined conditions.
ISO/IEC 17043:2023
Validation
Verification where the specified requirements are shown to be adequate for an intended use — demonstrating a procedure is fit for its purpose.
VIM (JCGM 200:2012) 2.45
Test accuracy ratio (TAR)
The legacy ratio of unit-under-test tolerance to the accuracy specification of the standard used. Superseded in rigorous work by the test uncertainty ratio, which accounts for the whole measurement process.
Industry practice
Proficiency testing
Evaluation of participant performance against pre-established criteria by means of interlaboratory comparisons — an ISO/IEC 17025 requirement for demonstrating ongoing competence.
ISO/IEC 17043:2023
Test uncertainty ratio (TUR)
The ratio of the tolerance of the unit under test to the expanded uncertainty of the measurement process used to test it. A 4:1 TUR is the traditional benchmark; lower ratios call for guard banding or risk analysis (ANSI/NCSL Z540.3).
ANSI/NCSL Z540.3