When working with clients that need accredited calibration services, ISO/IEC 17025 instructs laboratories on what is required for accredited calibration certificates in many sections, including 7.8.2.1, 7.8.4.1, and 7.8.6. These requirements are strengthened further by A2LA’s normative requirements for calibration providers in the document R205 – Specific Requirements – Calibration Laboratory Accreditation Program. With multiple sources of requirements for calibration certificates, the intent of this article is to shed light on some of the common non-conformances regarding calibration certificates.
Significant Figures
One of the most common nonconformances identified is listing significant figures incorrectly. Per R205 section 4.3, the laboratory shall meet the requirements of ILAC P14:09/2020 Policy for Uncertainty in Calibration sections 5.1 to 5.6. Here in section 5.3 of ILAC P14, the requirement for significant figures is given as follows:
“The numerical value of the expanded uncertainty shall be given to, at most, two significant digits. Where the measurement result has been rounded, that rounding shall be applied when all calculations have been completed; resultant values may then be rounded for presentation. For the process of rounding, the usual rules for rounding of numbers shall be used, subject to the guidance on rounding provided i.e in Section 7 of the GUM.”
This nonconformance typically occurs when organizations inadvertently list more than two significant figures due to using programs or templates that default to more than two significant figures, or in other cases, due to trailing zeros, as they are considered significant.
Measurement Uncertainty
The second common nonconformance related to the calibration certificates is when the organization lists a measurement uncertainty smaller than the CMC on their scope of accreditation. This requirement is defined in ILAC P14 section 5.5 as follows:
“As the definition of CMC implies, accredited calibration laboratories shall not report a smaller measurement uncertainty than the uncertainty described by the CMC for which the laboratory
is accredited.”
When preparing certificates for your organization, it is wise to take additional time to make sure the measurement uncertainty reported is truly greater than or equal to your CMC. Consider methods you could use to compare them, such as automated systems or publication checklists.
Another common issue regarding CMC is the indiscriminate use of the CMC as the measurement uncertainty of an actual calibration. Per R205, laboratories are not allowed to indiscriminately utilize the CMC listed on the scope of accreditation as the uncertainty being reported, as it is not justified.
Date of Issue
When preparing your certificates, please keep in mind that the date of issue shall be listed per ISO/IEC 17025: 2017 per section 7.8.2.1.j. Many times, we see organizations list the date of calibration but don’t list the date that the report/certificate was formally issued. Be sure to keep a close eye to make sure all dates are addressed, as required by ISO/IEC 17025 section 7.8.2.1.
Concise Language
Another common issue on certificates would be when laboratories do not properly state that the results only relate to the items tested, calibrated, or sampled. This language is critical per ISO/IEC 17025 section 7.8.2.1 and ensures that the results are not misconstrued as to what aspects are impacted or effected. Without this language, things become more unclear for clients on what was fully performed.
Traceability
One of the most important attributes of calibration certificates is ensuring proper traceability. As accredited calibration serves as a link in the traceability chain to the SI, we want to keep in mind two specific requirements that are commonly missed or listed incorrectly. Per ISO/IEC 17025, our specific calibration requirements call out that a statement must be listed identifying how the measurements are metrologically traceable. If we do not have a clear indication that the calibration is traceable, the concern arises that our customers do not know if the certificate acts as a link in the chain or not.
Along with this, many organizations make the claim of “NIST traceable.” When we make a claim of traceability, the language should not be focused on traceability to a specific national metrology institute but should be effectively communicating to the customer that the accredited calibration is traceable to the SI. These aspects are critical in ensuring that the work meets the customer’s needs and follows the appropriate requirements and language. Having these types of discussions is important to gain an understanding of whether they need something accredited, or just non-accredited but NIST traceable.
Clear Customer Communication
Along with the discussions highlighted earlier, we want to ensure that as laboratories, we are diligent in having meaningful discussions with our clients. By meaningful, we want to ensure the customer’s needs, the standard, and quality needs are met. A common disconnect is the method used, as well as how many test points are used.
Make sure that the method is properly identified on certificates per 7.8.2.1.f, but also ensure the method requested and used truly meets the customer’s needs. The most common disconnect is in calibrations utilizing multiple test points. A customer may ask for a calibration of a temperature measuring device to meet their needs and be traceable to a specific range. During the contract review, it is important to ensure that the appropriate number of test points are utilized to meet the customer needs. If the client needs the entire range covered, a single point calibration might not be appropriate, but something like a triple point calibration could be. A single point gives you an image at a single instance while the triple point using a low, medium, and high point in the range allows us to extrapolate the traceability for that entire range of the equipment. Discussions like these greatly help prevent recalls and establish the calibration needs clearly on both sides.
Speaking of both sides, when an instrument requires adjustment or repair, the before/after date must be properly listed per ISO 17025 7.8.4.1.d. Calibrations are done to establish comparisons. Understanding this relationship relies on having a proper understanding of how things were previously, and where they are at the end of the process.
Decision Rules
The final common nonconformity that we’ll mention comes from how decision rules are properly documented. As decision rules are a current point of contention in the world of metrology, A2LA has a more in-depth document titled G136 – Guidance on Decision Rules in Calibration, which goes into greater detail on this subject.
There are several technical and non-technical aspects that can be missed when generating accredited certificates for a client. Be sure to focus not only on what you do in the calibration and report processes to ensure proper results, but also make sure to have those candid discussions with clients to ensure everyone’s needs are met. Remember, taking extra time to have these discussions can assist in mitigating potential areas of risk related to accredited calibration certificates.