Acceptable traceability of a distributed national metrological system

Traceability of national standards to the international level, as well as the quality of the dissemination of these values to lower level working measurement standards has to meet primarily the requirements of a particular country, but equally importantly has to comply with strict and explicit rules of international accreditation bodies. In this respect vertical, hierarchically organised traceability links are usually properly evaluated in terms of added uncertainties, but horizontal connections, forming closed loops could be overlooked. It is essential to assure minimal influence from one physical quantity to another by proper uncertainty ratios. In many countries, especially in small and developing countries in transition period from one economic system to another, national metrology systems, as a key technology for development, production and technology transfer are often organised as distributed systems of laboratories; holders of national standards, as opposed to centralised systems, which are traceable to the international level, i.e. laboratories, where primary standards are realised. It is usually also not foreseen to realise SI units according to the definitions but on the highest level of transfer technology and disseminated with minimal additional uncertainties.