# Using Symbols to Tag Objects

There are many ways to use symbols in *Mathematica*. Here we use symbols as "tags" for different types of objects.

Working with physical units gives one simple example. When you specify the length of an object, you want to give not only a number, but also the units in which the length is measured. In standard notation, you might write a length as 12 meters.

You can imitate this notation almost directly in *Mathematica*. You can, for example, simply use a symbol to indicate the units of our measurement.

The symbol

here acts as a tag, which indicates the units used.

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You can add lengths like this.

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This converts to a speed in feet per second.

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There is a *Mathematica* package that allows you to work with units. The package defines many symbols that represent standard types of units.

Load the

*Mathematica* package for handling units.

The package uses standardized names for units.

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The function

converts to the specified units.

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Usually you have to give prefixes for units as separate words.

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