# Units and Standards

## Unit Conversions Between Systems

For many years, an effort has been made to have the metric system, including SI units, adopted worldwide. As early as 1866, the United States Congress legalized the use of the metric system. More than a hundred years later, in 1976, the Congress adopted the Metric Conversion Act, declaring it the policy of the nation to increase the use of the metric system in the United States.

In fact, little progress has been made in that direction. Indeed, elements of the British system of measurement continue in use for specialized purposes throughout the world. All flight navigation, for example, is expressed in terms of feet, not meters. As a consequence, it is still necessary for an educated person to be able to convert from one system of measurement to the other.

In 1959, English-speaking countries around the world met to adopt standard conversion factors between British and metric systems. To convert from the pound to the kilogram, for example, it is necessary to multiply the given quantity (in pounds) by the factor 0.45359237. A conversion in the reverse direction, from kilograms to pounds, involves multiplying the given quantity (in kilograms) by the factor 2.2046226. Other relevant conversion factors are 1 inch = 2.54 centimeters and 1 yard = 0.9144 meter.

## Resources

### Books

Adams, Herbert F.R. SI Metric Units: An Introduction. Toronto: McGraw-Hill Ryerson, 1974.

Jerrard, H.G., and D.B. McNeil. A Dictionary of Scientific Units: Including Dimensionless Numbers and Scales. London: Chapman and Hall, 1980.

Nelson, Robert A. SI: The International System of Units. Stony Brook, NY: American Association of Physics Teachers, 1982.

David E. Newton

## KEY TERMS

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British system

—A collection of measuring units that has developed haphazardly over many centuries and is now used almost exclusively in the United States and for certain specialized types of measurements.

Derived units

—Units of measurements that can be obtained by multiplying or dividing various combinations of the nine basic SI units.

Metric system

—A system of measurement developed in France in the 1790s.

Natural units

—Units of measurement that are based on some obvious natural standard, such as the mass of an electron.

SI system

—An abbreviation for Le Système International d'Unités, a system of weights and measures adopted in 1960 by the General Conference on Weights and Measures.