**GLP 4**

**Good Laboratory Practice**

**for**

**Periodic Recalibration of State Standards**

A number of States have provisions in their weights and measures laws
that require the periodic submission of their State standards to NIST
for calibration. Those provisions are based on an early version of the
Model Law (1911), which was considered appropriate for the circumstances
that prevailed prior to the establishment of the New State Standards
Program by NIST. Periodic calibration is necessary on a regular,
periodic basis, and also when measurement control results from internal
control charts or external round robins indicate questionable data.

Standards of mass, volume, and length, fabricated from modern materials,
kept in the controlled environment of a State metrology laboratory under
the custody of trained metrologists, are generally stable and not
subject to change. Moreover, the cooperative NIST‑State audit programs
often identify changes in ample time for corrective action in the
unlikely event that such a change should occur. These same programs
provide the necessary evidence of the ability to provide traceable
measurement results at a level of confidence sufficient for the need.

Moreover, the process of packing, shipping, and unpacking exposes the
standards to unnecessary hazards that could result in damage,
compromising their integrity. The return and re-calibration could take
several months causing an unavailability of State services that would be
disruptive to the performance of the mission of the State laboratories.

In order to develop a policy for the guidance of and implementation by
all 50 States regarding this subject, the following actions are
recommended:

> 1\. All States should recognize the fact that periodic return of their
> State standards to NIST for re-calibration is essential to comply with
> ISO/IEC 17025, GMP 11, and when: 1) data regarding traceability is
> unavailable; 2) charted measurement results indicate that the
> standards are out of control; 3) measurement results on round robins
> or performance tests are suspect; or 4) NIST advises the State of the
> need.
>
> 3\. References to the periodic re-calibration of State standards in
> the law such as,
>
> \"He (the director) shall maintain the State standards in good order
> and shall submit them, at least once in ten years, to the National
> Institute of Standards and Technology for calibration,\"
>
> should be followed if present and may be amended to reflect a regular
> interval, plus identified needs. In lieu thereof, the wording of
> Sections 3 and 12 of the present Uniform Law may be substituted:

SECTION 3. [PHYSICAL STANDARDS]{.underline}. ‑- Weights and measures
that are traceable to the U. S. prototype standards supplied by the
Federal Government, or approved as being satisfactory by the National
Institute of Standards and Technology, shall be the State primary
standards of weights and measures, and shall be maintained in such
calibration as prescribed by the National Institute of Standards and
Technology. All secondary standards may be prescribed by the director
and shall be verified upon their initial receipt and as often thereafter
as deemed neces­sary by the director.

SECTION 12. [POWERS AND DUTIES OF THE DIRECTOR]{.underline}. ‑‑ The
director shall:

12 (a) Maintain traceability of the State standards to the National
Institute of Standards and Technology, *as evidenced by laboratory
Recognition.*

The approach described above is recommended by NIST because each State
that participates in the Weights and Measures Division Laboratory
Recognition Program has the capability of evaluating its own State
standards with the necessary documentation referencing the national
standards. The Laboratory Recognition Program provides interaction
between the State standards labora­tories and NIST, ensuring satisfactory
laboratory conditions suitable for primary standards in addition to the
proper use of NIST procedures in standards calibration. Thus, each State
program is evaluated and, if found in compli­ance, is Recognized as being
capable of performing the measurements listed on the Certificate of
Measurement Traceability.