**SI Units**

The unit system emphasized in this book is the International System of Units (SI). The three physical quantities displayed in Table I-I are used in the early chapters. Standards, which must be both accessible and invariable. have been established for these base quantities by international agreement. These standards are used in all physical measurement, for both the base quantities

and the quantities derived from them. Scientific notation and the prefixes of Table 1-2 can be used to simplify measurement notation in many cases.

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