IJCA Vol 5 Issue 1 - Flipbook - Page 35
2026 | Volume 5, Issue 1
Here is an example:
- Level 0 are SI units defined by fixed
numerical values of fundamental constants.
Measurement uncertainty at this level is zero.
- Level 1 is the national primary standard: the
artifact, device, or realization with the highest
metrological qualities in its field, based level
zero materialization.
The International Journal of Conformity Assessment
uncertainty, and periodic reassessment—key
features of robust accreditation processes.
The following figure illustrates how these
principles come together in practice by showing a
typical mass traceability hierarchy, including levels
of standards, comparison methods, uncertainties,
and calibration intervals.
- Level 2 holds the secondary standards,
established by direct comparison with the
primary. When a secondary is used to calibrate
lower-order standards, it functions as a
reference standard.
- Level 3 contains third-order working standards,
obtained by comparison with those reference
standards. Working standards at this level
verify ordinary instruments of lower accuracy
or calibrate other working standards; when they
do, they are treated as reference standards and
conserved so that their comparisons back to
Level 2 need not be frequent.
- Level 4 comprises the broader population of
working standards, themselves maintained by
comparison to Level 3.
A good traceability chart makes this structure
transparent. It identifies the standards at each
level, documents their sources and certificates,
and states the uncertainties—specifically the
limits on freedom from bias, (the residual
systematic error that may still be present) —that
must not be exceeded as results are disseminated
downward or verified upward. When the chart is
combined with competent practice, scheduled
re-calibrations, robust documentation, and a
functioning measurement assurance program, the
result is a measurement system whose numbers
can be trusted—because they can be traced.
Why Traceability Matters in Conformity
Assessment
As the “backbone” of a measuring system,
traceability ensures uniform measurement
across applications and markets and enabling
acceptance of results beyond organizational or
national borders. In practice, it functions as the
unit’s “genealogy” or “chain of custody,” ending at
the point of application in manufacturing, services,
and legal metrology.
Within laboratory accreditation and certification
ecosystems, traceability is an expectation under
ISO/IEC 17025 and related schemes, and is
intertwined with competence, suitable procedures,
Figure 2. A proposed traceability chart satisfying quality,
technical and accreditation requirements.
Note: Following the 2019 rede昀椀nition of the SI, the kilogram is
de昀椀ned by the 昀椀xed numerical value of the Planck constant
(h) and realized through primary methods such as the Kibble
balance. The International Prototype of the Kilogram (IPK)
is no longer the de昀椀ning reference and is retained solely for
historical continuity and comparison.
Calibration Hierarchies and Charting
Traceability
A calibration hierarchy (or traceability chain)
typically flows from primary standards (Level
1), to secondary/reference standards (Level 2),
to working standards (Level 3–4), and then to
ordinary instruments at the application level.
Effective charts document standards used,
uncertainty budgets, measurement assurance,
and calibration intervals at each level.
References and dissemination
Traceability may start “from the top down”
(primary to application) or be verified “from the
bottom up” (application to national standard).
In all cases, adjacent elements and associated
uncertainties must be identified and quantified.
Documentation and responsibilities
Calibration providers must supply traceability
statements and uncertainty in reports; users
must critically assess claims (e.g., by evaluating
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