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It is also important to realize that science is in the business of measuring things. This means that, unlike a math class, any number you see is a measurement of something and has a unit attached to it. So we never have $$9.5$$ but we can have $$9.5$$ centimeters or a frequency of $$9.5$$ hertz ($$\text{Hz}$$). This book uses the metric system but other sets of units are mentioned. Here is a useful site that converts metric units to other systems: Conversion Calculator.