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SI Units 

SI Units

Units of Measure

Phil B. Fontanarosa

and Stacy Christiansen

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SI Units

The International System of Units (Le Système International d'Unités or SI) represents a modified version of the metric system that has been established by international agreement and currently is the official measurement system of most nations of the world.1 The SI promotes uniformity of quantities and units, minimizes the number of units and multiples used in other measurement systems, and can express virtually any measurement in science, medicine, industry, and commerce.

In 1977, the World Health Organization recommended the adoption of the SI by the international scientific community. Since then, many biomedical publications throughout the world have adopted SI units as their preferred and primary method for reporting scientific measurements. However, in the United States, most physicians and other health care professionals use conventional units for many common clinical measurements (eg, blood pressure), and many clinical laboratories report most laboratory values by means of conventional units. Accordingly, some biomedical publications, including JAMA and the Archives Journals, have adopted an approach for reporting units of measure that includes a combination of SI units and conventional units. (See 18.5, Conventional Units and SI Units in JAMA and the Archives Journals.) Authors, scientists, clinicians, editors, and others involved in preparing and processing manuscripts for biomedical publication should be familiar with appropriate use of units of measure and should ensure that the presentation and reporting of scientific information is clear and accurate, including any necessary conversion from conventional units to SI units, or vice versa.

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