How much does the SI, namely the proposed “New SI”, conform to principles of the Metre Treaty?
The International System of Units (SI) was first adopted in 1960, as the more recent implementation of the Metre Treaty signed in 1875. Basic features of the original SI are that (a) seven units are chosen as “base units”, all the others being “derived units”, and (b) the definitions of the base units should not create interdependence. This way, the SI conforms to the basic principle of the Metre Treaty that each signatory country can realise its choice of primary national standards of the very definitions of the units without needing to resort to calibrations obtained from another country, and without obligation to have them realised for all the units. A mismatch already occurs to some extent with respect to the above features in the present definitions of SI base units. This contribution, strictly based on metrological considerations, illustrates how the present proposal concerning new definitions for the base units, called “New SI”, would extend the mismatch. In this frame, also the meaning is discussed of the concepts of hierarchy and traceability in metrology. By outlining some of the consequences, a discussion is stimulated related to the status of base unit, to the meaning of calibration at the level of the standards of the unit definitions, and to the interdependence of countries’ standards.
KeywordsBase units Calibration Fundamental constants Hierarchy Metre Treaty SI
- 1.Bureau International des Poids et Mesures. http://www.bipm.org/en/convention/. See: Metric Convention of 1875, Paris, 20 May 1875 http://lamar.colostate.edu/~hillger/laws/metric-convention.html
- 2.Bureau International des Poids et Mesures, SI Brochure. http://www.bipm.org/en/si/si_brochure/
- 3.CCU (2013) Draft 9th SI Brochure. Bureau International des Poids et Mesures http://www.bipm.org/en/si/new_si/:si_brochure_draft_ch123_131216
- 9.CIPM (1999) Mutual recognition of national measurement standards and of calibration and measurement certificates issued by national metrology institutes (MRA). Bureau International des Poids et Mesures, Sèvres. http://www.bipm.org
- 10.Pavese F (2013) Mathematical and statistical tools in metrological measurement. In: Physical methods, instruments and measurements [UNESCO-EOLSS Joint Committee Ed]. Encyclopedia of Life Support Systems (EOLSS), Developed under the Auspices of the UNESCO, Eolss Publishers, Oxford, UK. http://www.eolss.net
- 11.Bureau International des Poids et Mesures. http://kcdb.bipm.org
- 12.BIPM (2012) International vocabulary of basic and general terms in metrology (VIM), 3rd edn. BIPM/ISO, JGCM 200:2012. 2008 version with minor corrections. http://www.bipm.org/en/publications/guides/vim.html
- 14.Pavese F (2014) Metrologia 51:L1–L4, with online Supplementary InformationGoogle Scholar
- 16.Bureau International des Poids et Mesures. http://www.bipm.org/en/si/new_si/mise-en-pratique.html
- 20.Consult. http://www.metrologybytes.net
- 24.Bronnikov KA, Melnikov VN (2011) Meas Tech 53:1196–1203Google Scholar
- 26.Physikalisch-Technische Bundesanstalt. http://www.ptb.de/cms/en/fachabtellungen/fb-44/ag-441/realisation-of-the-si-second/history-of-the-unit-of-time/ (consulted 2013.11.29)