Summary Note
Key concept recap
Introduction to Measurement
Measurement is the foundation of quantitative science. Every measurement involves comparison with a reference standard called a unit, and the result is expressed as a number accompanied by that unit. Without a well-defined and universally accepted unit, it would be impossible to communicate or compare measurements made in different places or at different times. Physical quantities are interrelated through mathematical laws, so only a limited set of independent, fundamental quantities is needed to express all other quantities.
The units chosen for these fundamental (base) quantities are called fundamental or base units. All other quantities are derived from them, and their units — called derived units — are expressed as combinations of the base units. A complete, self-consistent collection of base units and derived units forms a system of units. The adoption of a globally accepted system is essential for science, engineering, and international trade.