SI Guide to international language of measurement

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ISO has just published a new version of the SI Guide, a small manual for the use of the SI, the International System of Units (Système International d’Unités).

The SI is a comprehensive metric and decimal system based on units and derived units. The seven base units are: length, mass, time, electric current, thermodynamic temperature, amount of substance, and luminous intensity.

This new edition of the SI Guide includes for the first time:

- one new SI derived unit: the katal, symbol kat (1 kat = 1 mol/s) for the quantity of catalytic activity – essentially used in clinical chemistry, it can also be used in other fields of chemistry

- prefixes for binary multiples used in information technology, to be distinguished from the decimal SI prefixes.

The metric system was internationally adopted through the Metre Convention which was signed by 17 nations in 1875 in Paris, France. Today 51 nations have signed and the name of SI to this system was given in 1960 at the 11th General Conference on Weights and Measures. SI is the only system of units recognized worldwide and so has the advantage of establishing a universal language of measurement.

The SI is built in such a way that only one unit is used for each kind of quantity, which makes the system very simple. It is used everywhere in all contexts: in daily life, just as in the technical and scientific fields.

The SI Guide with its pocket format contents the essence of the International System of Units and covers:

  • the historical background
  • the principles of the SI
  • the base units
  • derived units
  • multiples and sub-multiples
  • additional units
  • quantities and units
  • printing rules
  • space and time
  • periodic phenomena
  • mechanics
  • heat
  • electromagnetism
  • light
  • acoustics
  • physical chemistry
  • atomic and nuclear physics
  • ionizing radiations
  • characteristic numbers
  • information technology
  • conversion factors.

The 32-page SI Guide will be useful for many people including engineers, scientists, technical writers, teachers and students.

The information in the guide is based on the International Standard ISO 31, Quantities and units, now being successively replaced by the ISO 80000 and IEC 80000 series.

The SI Guide costs eight Swiss francs and is available from ISO national member institutes (see the complete list with contact details) and from ISO Central Secretariat through the ISO Store or by contacting the Marketing & Communication department (see right-hand column).

Sandrine Tranchard
Sandrine Tranchard

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