Soda is commonly sold in 2-liter "3ottles-an example of the use of units in everyday life. 1.3 Units of Measurement 9 1.3 ~ Units of Measurement Making observations is fundamental to all science. A quantitative observation, or mea-surement, always consists of two parts: a number and a scale (called a unit). Both parts must be present for the measurement to be meaningful. In this textbook we will use measurements of mass, length, time, temperature, elec-tric current, and the amount of a substance, among others. Scientists recognized long ago that standard systems of units had to be adopted if measurements were to be useful. If every scientist had a different set of units, complete chaos would result. Unfortunately, different standards were adopted in different parts of the world. The two major systems are the English system used in the United States and the metric system used by most of the rest of the industrialized world. This duality causes a good deal of trouble; for exam-ple, parts as simple as bolts are not interchangeable
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