Integral to the support of calibration standards, are traceability and uncertainty.
Traceability in the context of measurement science means that when the result of a measurement is said to be traceable (normally to a national authority such as NIST), there exists:
- a known valid relationship to internationally or nationally recognized standards.
- a thoroughly documented "unbroken chain" of reference to the measurement authority.
There are no fewer than five methods of establishing traceability, and sometimes a measurement is rendered traceable via multiple methods. Most of VLSI Standards' products are traceable by method 1. Method 1 occurs when a laboratory acquires Standard Reference Materials (SRMís) from NIST or another international authority, and uses these as the laboratoryís primary standards for calibration of the instruments used by that laboratory.
There are many motivations to ensure traceability in measurement. These range from the need to comply with stated contractual requirements to the desire to use the best possible practices in measurement. The objectivity of a neutral third party is often valued in negotiations or disputes between suppliers and purchasers, and the requirement of traceability can avoid potential disagreements or misinterpretations of data.
One of the most frequently asked questions associated with physical standards in all industries is what does the value of uncertainty on the calibration certificate mean? After all, "uncertainty" sounds like the last thing you would want associated with your accurate calibration standard. Upon closer examination, however, stated values for uncertainty become an asset to the user, rather than a weakness in the standard.
The statement of uncertainty represents the highest possible quality of the measurement process. The value for uncertainty, as it turns out, represents the care and diligence that are taken in quantifying all possible sources of imperfection in a measurement used to certify a standard.
Since 1993, VLSI Standards has updated all product documentation and associated algorithms to meet the requirement defined in the Guide to the Expression of Uncertainty in Measurement. These improvements reinforce the rigor and the traceability of our certified products, and provide complete documentation of both the measurement process and the evaluation of the measurement data.
Click here to read the NIST paper entitled "Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results" in a new browser window.