Metric Conversion Factors

The metric system of units, officially known as the International System of Units, or SI, is used throughout this book, with the single exception that angular measurements are usually expressed in degrees rather than the SI unit of radians. By international agreement, the fundamental SI units of length, mass, and time are defined as follows (see, for example, NBS Special Publication 330 [NBS, 1974]): The metre is the length equal to I 650 763.73 wavelengths in vacuum of the radiation corresponding to the transition between the levels 2p10 and 5d$ of the krypton-86 atom.

The kilogram is the mass of the international prototype of the kilogram (a specific platinum-iridium cylinder stored at Sevres, France). The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the cesium-133 atom. Additional base units in the SI system are the ampere for electric current, the kelvin for thermodynamic temperature, the mole for amount of substance, and the candela for luminous intensity. Mechtly [1973] provides an excellent summary of SI units for scientific and technical use.

The names of multiples and submultiples of SI units are formed by application of the following prefixes:

Factor by which

is multiplied

Prefix

Symbol

I012

tera

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