What PROFICIENCY TESTING means to the customer of calibration.



It must be audit season

It seems like the middle of May every year when the phones start ringing for our Quality Manager. Customer requests for changes on certificates, explanations of methods, definitions of standards, and a whole host of other questions begin to roll in well into fall when things start to quiet down a bit.

How do you know its RIGHT?

 Every now and then we will find ourselves drawn into a disagreement between one of our customers and their auditors, and the question that always comes up is, “how do you know it’s right?” So, at this point we all go into our own versions of a speech we keep tattooed in our memory banks. “We are an ISO 17025 Accredited organization, we have proven competency in the eyes of an internationally recognized accreditation body, all of our senior technicians are ASQ Certified Calibration Technicians, and we maintain a direct path of traceability to the SI including all data and uncertainties.” Most of the time, that answers the question, but on occasion…

How do we REALLY know its RIGHT?

Easy, we participate in proficiency testing programs. Proficiency testing is used all across the scientific and measurement community to objectively compare measurement results across multiple organizations. In the world of metrology proficiency testing has a simple progression.

PROFICIENCY TESTING alliance calibration


When the final report is issued, the calibration company reviews the normalized errors for the measurements performed. We call them En values (E-sub-n), and they should be between -1 and 1. This means that the values match within the stated measurement uncertainties.

PROFICIENCY TESTING alliance calibration


The pivot lab is typically a higher echelon lab that can achieve tighter uncertainties than typical commercial calibration labs, and this is done to improve the quality of the measurement results and therefor the final PT outcomes.

PROFICIENCY TESTING alliance calibration
PROFICIENCY TESTING alliance calibration

 The circle for the calibration lab is larger than the pivot lab to represent the magnitude of the uncertainty







Proficency testing and audits/assesments

ISO 17025 does not expressly require proficiency testing, (ISO/IEC 17025 5.9.1)however most accreditation bodies (ABs) do. This gives the ABs the ability to assess measurement results objectively using real world data. This also gives the calibration laboratory the ability to recognize potential measurement errors before they become a problem. Ongoing proficiency testing can identify drift or degradations in systems that might be missed in a calibration alone because proficiency testing looks at the calibration process not just the calibration standards. In this way, it works as a version of method validation, as well as measurement validation.

What does this mean to the customer?

A calibration provider that has a robust proficiency testing program adds an additional level of confidence that calibration results are valid. At Alliance, we go beyond the basic proficiency test requirements and have multiple technicians perform the tests in a “blind” manner and compare all technician results when we receive the final PT reports. Proficiency testing ultimately reinforces the laboratory’s traceability chain and ensures the customer is receiving what they ultimately paid for, traceability for their instruments and artifacts.


Download the ILAC Brochure on the benefits of Proficiency Testing

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