Using the SI System of Units

1975 ◽  
Vol 48 (1) ◽  
pp. 1-13 ◽  
Author(s):  
F. S. Conant
Keyword(s):  
Entire System ◽  
International Agreement ◽  
Conversion Factors ◽  
Electric Conductance ◽  
Si Units ◽  
System Of Units ◽  
The Difference ◽  
Base Units

Abstract SI surpasses previous metric systems in coherence, simplicity, distinction between force and mass, choice of units, and uniformity of usage. Coherence eliminates conversion factors, other than powers of ten, within the system. Through simplification, only seven base units, two supplementary units, fifteen named derived units, and fourteen prefixes are needed to describe the entire system. Introduction of the newton as a unit of force and retention of the kilogram for mass clarifies the difference between the two quantities. Other new units are: pascal for pressure, Siemens for electric conductance and mole for amount of a substance. International agreement minimizes proliferation of specialized units or usage. Adopted conventions include spelling, abbreviations, style, and usage, as well as definitions for the units. Tolerances, rounding of numbers, and elimination of the comma in multidigit numbers assume new significance. Conversion to SI offers a unique opportunity to reduce the number of sizes of many products. Several schemes for metric modularism have been developed for this purpose. In changing from conventional to SI units the key idea is “think metric” rather than use dual dimensioning.

scholarly journals Quantity Calculus, Fundamental Constants, and SI Units

2018 ◽  
Vol 123 ◽  
Author(s):  
Barry N. Taylor
Keyword(s):  
International System ◽  
Fundamental Constants ◽  
Weights And Measures ◽  
International System Of Units ◽  
Si Units ◽  
System Of Units ◽  
Revised Si ◽  
Base Units ◽  
New Si

A revised International System of Units (SI) is expected to be established by the 26th General Conference on Weights and Measures when it convenes in November 2018 and to be put into practice starting on 20 May 2019, World Metrology Day. In consequence, the article published in this journal in 2011, “The Current SI Seen from the Perspective of the Proposed New SI,” is updated in this paper, which provides an opportunity to again demonstrate the usefulness of the quantity calculus in dealing with quantities and units. The quantity calculus and the seven defining constants of the current and revised SI are reviewed, and expressions for the seven current and revised SI base units are given. Relationships between the magnitudes of revised and current SI units and expressions for the numerical values of current SI defining constants expressed in revised SI units are also obtained using the quantity calculus.

scholarly journals SI-2019 and prospects for improving the accuracy of electrical measurements

2021 ◽  
pp. 35-39
Author(s):  
Iurii Pavlenko ◽  
Alexander Kolbasin ◽  
Olena Vаsileva
Keyword(s):  
International System ◽  
Fundamental Constants ◽  
Electrical Measurements ◽  
International System Of Units ◽  
Si Units ◽  
Accuracy Of Measurements ◽  
System Of Units ◽  
Measurement Units ◽  
Physical Laws ◽  
Base Units

Increasing requirements for the accuracy of measurements have led to the need to revise the existing International System of Units (SI). The important element of the SI-2019 reform is “the establishment of the SI base units through seven defining constants, the numerical values of which are fixed”. The approach to the establishment of the measurement units has fundamentally changed. If earlier a definition was given of how the unit is realized, now only the exact numerical values of the fundamental constants are fixed, and their values are expressed in the corresponding SI units. Measurement units are determined on the basis of known physical laws, which include certain fundamental constants. The article analyzes the changes in SI-2019 related to electrical measurements, and also discusses the prospects for the development of accurate electrical measurements.

SI Units

PEDIATRICS ◽  
1989 ◽  
Vol 83 (1) ◽  
pp. 129-131
Author(s):  
Keyword(s):  
United States ◽  
American Medical Association ◽  
Scientific Communication ◽  
The United States ◽  
Coherent System ◽  
Common Language ◽  
Si Units ◽  
Drug Concentrations ◽  
Significant Figures ◽  
Base Units

Le Systeme International d'Unites or SI units is a system of measure that is an outgrowth of the metric system, widely used in countries other than the United States. This system comprises seven base units from which all other measurements are made (Table). The aim of SI units is to (1) provide a coherent system of measure, (2) ensure that quantities and units are uniform in concept and style, and (3) minimize the number of multiples and submultiples in common use. A more complete review of metrification and SI units has been published in this journal. The conversion to SI units was mandated in December 1984 by the American Medical Association House of Delegates to "provide physicians and other scientists in the United States with an improved common language for fluent scientific communication between nations as well as between sciences." In several published articles there have been suggestions that the United States should, during the next year, begin uniformly reporting laboratory test data in SI units, including drug concentrations in molar units. Although drugs would continue to be prescribed in mass units, the desirability of prescribing and dispensing drugs in molar units has been suggested. The focus of this commentary is to summarize the problems and inconsistencies of expressing drug concentrations in molar units, assuming that prescribing and dispensing would continue in mass units. PHARMACOKINETIC CALCULATIONS In a recent study tenfold dosing errors were demonstrated, resulting from mathematical miscalculations while using traditional units. The introduction of additional calculations for conversion to SI units, and the fact that SI units involve decimal places with several significant figures, will likely magnify this type of error.

scholarly journals Adapting the International System of Units to the twenty-first century

2011 ◽  
Vol 369 (1953) ◽  
pp. 3907-3924 ◽  
Author(s):  
Ian M. Mills ◽  
Peter J. Mohr ◽  
Terry J. Quinn ◽  
Barry N. Taylor ◽  
Edwin R. Williams
Keyword(s):  
International System ◽  
International Committee ◽  
First Century ◽  
Weights And Measures ◽  
International System Of Units ◽  
System Of Units ◽  
Elementary Charge ◽  
Magnetic Constant ◽  
Base Units ◽  
New Si

We review the proposal of the International Committee for Weights and Measures (Comité International des Poids et Mesures, CIPM), currently being considered by the General Conference on Weights and Measures (Conférences Générales des Poids et Mesures, CGPM), to revise the International System of Units (Le Système International d'Unitès, SI). The proposal includes new definitions for four of the seven base units of the SI, and a new form of words to present the definitions of all the units. The objective of the proposed changes is to adopt definitions referenced to constants of nature, taken in the widest sense, so that the definitions may be based on what are believed to be true invariants. In particular, whereas in the current SI the kilogram, ampere, kelvin and mole are linked to exact numerical values of the mass of the international prototype of the kilogram, the magnetic constant (permeability of vacuum), the triple-point temperature of water and the molar mass of carbon-12, respectively, in the new SI these units are linked to exact numerical values of the Planck constant, the elementary charge, the Boltzmann constant and the Avogadro constant, respectively. The new wording used expresses the definitions in a simple and unambiguous manner without the need for the distinction between base and derived units. The importance of relations among the fundamental constants to the definitions, and the importance of establishing a mise en pratique for the realization of each definition, are also discussed.

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