# The Notion of Units

A "unit" is a word or concept defining a system of measurement.  When making or describing a measurement, units define the system of measurement to use when interpreting the measurement's magnitude.  For example, both "inches" and "miles" are units of length.  A measurement of "5 inches" and "5 miles" have the magnitude "5" in common, but the different "units" define how different the two measurements actually are.

Not all problems need to refer to units.  If every measurement of the same type (e.g. length) uses the same units throughout the entire discussion, the units can be left off entirely.  For example, the following two phrasings are equivalent, since the same unit of length is used throughout:

1. How many unit inches is three unit inches added to twelve unit inches?
2. How many is three added to twelve?

A problem needs to include units when two or more measurements of the same type (e.g. distance) use different units of measurement.  Also, if units are given for a type of measurement, make sure every measurement of that type includes its units.

AutoMathic supports two major techniques for using units:

A common task with math problems is unit conversion, i.e. switching from one system of measurement to another...  Unit conversion is also easy with AutoMathic, but temperature conversion has some special requirements: