Are all Metrology Labs Alike?

Short answer – NO!!!

In fact, to those of us in the industry who truly know what it takes to recalibrate instruments to objectively defined standards, a better question might be— Are you using the equivalent of a meat thermometer to validate conditions in your processing plant or laboratories?

There are two industry trends that have combined to jeopardize the quality standards in many pharmaceutical processing operations, whether recognized or not. The first is the proliferation of mom and pop metrology labs that do not adhere to rigorous third party accreditations. The second is the growing popularity of on-site calibration services, which are inherently disadvantaged at matching the standards achieved by those using less mobile but more sophisticated testing apparatus.

Best Measurement Uncertainty
The first step in making an apples-to-apples comparison of metrology lab services is to ask for what is called the “best measurement uncertainty” of each service.

What’s ‘best measurement uncertainty’?

In 1978, a nonprofit organization, the American Association for Laboratory Accreditation (A2LA) was established as a public service for all in need of standardized and reliable testing standards. One might think that all metrology labs are A2LA-accredited, but one should think again. Getting A2LA accreditation takes time and resources, and many metrology labs, especially the great number of mom and pop type operations that have spawned in the last few decades, have not gone through the rigors of A2LA accreditation.

A2LA accreditation involves giving you what is called a “scope” that defines the best a particular metrology lab can do. The ‘best measurement uncertainty’ takes into account the ENTIRE system affecting the measurements—the quality of the equipment, the quality of test chambers, personnel training, etc. This quality rating—the ‘best measurement uncertainty’—is a way in which the A2LA accreditation is quantified.

NAVLAP is a commonly recognized equivalent of A2LA. But when a calibration lab tells you they are “NIST traceable” it doesn’t mean much. “NIST” isn’t a standard you can adhere to. A very significant number—in some areas the majority of so-called calibration services—cannot document their ‘best measurement uncertainty’ and quality managers can use ‘best measurement uncertainty’ documentation as a quick way to do a first cut between the wheat and the chaff.


Single vs. Full CalibrationsIn some cases, it is not only the quality of the metrology service being hired but also the nature of the instrument itself that needs to be considered. This is especially the case when full calibrations are needed of instruments using proprietary software. If proprietary software is involved, only manufacturers and others with access to the proprietary code can even begin to do a full calibration.

A full calibration is when a lab or manufacturer takes an instrument and checks it from the top to bottom and in between. More limited calibrations only look at a single point on the range, or sometimes two-point range. More limited calibrations have the potential to accurately set instruments for the designated points but to pull the instrument out of range at other points. It’s especially easy to be accurate at one point, but full scale adjustments take a bit more doing.

This is especially the case with calibrating humidity measuring instruments, which on the whole are a bit more challenging to calibrate compared to temperature monitoring instruments. Our independent testing suggests that with humidity calibrations there is a much wider difference between what a lab says it can do under perfect conditions and what it does in practice. One contributing factor is the relatively high costs of instruments that can calibrate across the entire range of humidity conditions important in the pharmaceutical industry—from the very dry to the most humid. Truth is, the vast majority of metrology services use instruments with a much narrower range than what is required.

Mobile metrology services are typically even more limited in their ability to calibrate humidity monitoring instrumentation. The instruments one needs to use to calibrate for humidity are usually the size of a household stove and difficult to move from one location to another, especially since they are often delicate instruments. Moreover, humidity calibration is a relatively time-consuming process, and on-site services often do not allow the time it actually takes to do accurate humidity calibrations.

Theoretically, even if an on-site metrology service is using top notch equipment there is still an objective disadvantage in not being able to control the testing environment. Instrumentation used for recalibrating humidity monitoring instruments is especially susceptible to environmental variance. Off-site metrology lab services, to the extent that they can do create controlled laboratory conditions obviously have an advantage.

Attractive as on-site recalibrations might sound, the convenience factor of avoiding shipping instruments hither and yon DOES have a likely price of less accuracy. True, if your prime concern is getting affidavits from a metrology lab that will help keep the FDA at bay, the type service that can come into your lab and measure /recalibrate all instrumentation is markedly more convenient. If quality concerns are more substantial, however, such that your operation truly needs to ensure the highest and most objective standards are adhered to in processing and laboratory testing alike, you probably want to ensure that the lab apparatus being used to calibrate humidity instruments are truly top notch. Here too, you get what you pay for, or rather, you get what your metrology lab has paid for.


Generalists vs. Specialists

Even more troublesome is the tendency of some metrology labs, even very small ones, to offer themselves as the proverbial “jack of all trades, master of none”. These services will not only recalibrate temperature, pressure, and humidity, but also all electronic devices used in a pharmaceutical lab or processing plant. Sounds good, but if you truly consider the type of capital investments required to get the best instrumentation available to recalibrate for the different properties, you begin to get an insight as to why there might be a wide variation in metrology lab testing results, especially for those without NAVLAP or A2LA accreditation. It also suggests why manufacturers of testing and monitoring instruments, if they do provide calibration services, sometimes have an advantage in that the same equipment and instrumentation investments they need to make for product development are also used for recalibrations.

Sticking to Standards

There is a tangential point of interest to the question of “Are all metrology labs alike”, and that is, “Do all quality managers in pharmaceutical processing operations require the same level of calibration accuracy?” What we can report on this issue has somewhat troublesome implications. For many years now, Dickson has conducted extensive surveys of what pharmaceutical companies’ quality manuals mandate for temperature and humidity monitoring and calibration standards, to help guide our product development initiatives. What most quality managers report is that two (or more) point span calibrations are essential and that pre-recalibration accuracy (i.e. before data) needs to be established for all instruments during recalibrations. (and compliance to strict calibration and testing standards like ANSI z540 or ISO 17026). However, what our sales records indicate is that the actual orders for calibrations do not match the written standards of quality manuals, e.g. before data measurements are often omitted.

Similarly, it is not uncommon for Dickson to be approached by pharmaceutical quality managers that employed sub-standard third party metrology labs who then want to know if pre-adjustment instrument performance, i.e. before data, is retrievable, which it is not once any recalibration has been made.

All this means that you have to truly think through real calibration requirements and thoroughly investigate the REAL capabilities of the metrology lab sources you plan to hire.

First things first of course-- NEVER SKIP REQUIRED RECALIBRATIONS. This means putting in processes that will allow your company to adhere to calibration schedules despite personnel shifts, vacations, or the unexpected. Reputable manufacturers that stand behind their products’ performance offer no-strings- attached free reminder services such as those provide by the Dickson Calibration Club®.



Chris Sorensen is VP of Dickson Company (, which offers the widest range of data loggers and chart recorders available in the world for pharmaceutical and other applications.


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As published in Pharmaceutical Processing magazine (9/2007).