This is a ruler.  The ruler represents unit 1 by displaying dimensional analysis.  Dimensional analysis is an organized way to convert units.  This ruler has many different kinds of units.  It uses some important metric and English units that are often used in dimensional analysis.  These are inches, feet, millimeters, and centimeters.  It displays many different kinds of conversions all in one place.  Rulers make it easy to use convert units by providing a visual aid.  It is easy to see how units fit into each other on a ruler.  For example, one can easily tell that there are 12 inches in a foot just by glancing at a ruler.  Using a ruler saves the time normally wasted writing out equations to convert distances.