Metrological reference

In this chapter I use the term metrological traceability to refer to the property of a measurement result that relates the result to a metrological reference. The word metrological is used to distinguish the concept from other kinds of traceability, such as the paper trail of documentation, or the physical trail of the chain of custody of a forensic sample. When the term traceable standard is used to refer to a calibration material, for example, the provenance of the material is not at issue, but the quantity value embodied in the standard. 

A metrological reference is a document defining (usually) a unit. A rational quantity scale, of quantities that can be compared by ratio and have a zero (e.g., length, mass, amount of substance, but not temperature in degrees Celsius), must have a unit, even if it is 1. 

A direct consequence of metrological traceability is that if two measurement results are metrologically traceable to the same metrological reference, then they must be comparable (i.e., can be compared) within their measurement uncertainties. This is sometimes explained in terms of the futility of... 

The foregoing discussion identifies the need for comparability and its achievement by metrological traceability. Comparability of measurement results is conveniently defined in terms of metrological traceability. If two results are traceable to the same stated metrological reference, then they must be comparable. Please note that in common speech comparable often means about the same magnitude, but this is not the case here. In the laboratory comparability of measurement results means simply that the results can be compared. The outcome of the comparison, whether the results are considered near enough to be equivalent, is not a factor in comparability here. 

The first criterion is that the measurements must be made in the same units—that is, traceable to the same metrological reference. This sounds obvious, but without attention to metrological traceability of a measurement... 

At the top of the traceability chain is the stated metrological reference, which for our purposes is the definition of a unit. It might not be obvious how a piece of paper from Paris giving the interesting, but rather esoteric, definitions of the SI base units can be used as a reference. The metrological reference allows the creation of a primary calibrator that embodies the value of the unit (or some multiple or submultiple of it). The international prototype... 

Input quantity Units (metrological reference) Relative standard uncertainty Traceability statement... 

Report metrological traceability. Measurement reports may require details of the metrological traceability chain or at least a statement of the metrological reference. 

The protocols for links to higher-level RMs and, generally, to the SI must be supplied by the producer of those RMs, or by a recognized (metrological) reference laboratory. 

Traceability is not really a new fundamental concept in the field of laboratory medicine. Many years before the concept traceability had been mentioned in general chemical metrology, reference measurement procedures and reference materials had been established in clinical chemistry. Some basic experimental work for the development of reference measurement procedures and reference materials had already been undertaken in expert laboratories. 

The revised edition of the VIM (VIM3), will probably ne-tune the term for traceability of a measurement result to be named metrological traceability. It is also likely that this de nition is improved to read something like property of a measurement result relating the result to a stated metrological reference through an unbroken chain of calibrations or comparisons each contributing to the stated measurement uncertainty. ... 

Metrological traceability of chemical measurement results means the establishment of a relation to a stated metrological reference (a trace). This can be the de nition of a measurement unit which, of necessity, must go through a practical realization or (better an embodiment) of that... 

Functional correlation in surface metrology refers to the relations between the surface and phenomena that influence or are influenced by the topography. Establishing functional correlations is one of the principal objectives of research in surface metrology. 

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