The AddUnit(unit, opts) function adds a new unit to or modifies options of an existing unit in the Unit Converter.

If the dimension corresponding to unit is not in the Unit Converter, the command Units[Converter][AddDimension](convert(unit, 'dimensions', 'base')) is executed automatically.

This procedure accepts symbols and variations in spelling. For example, $\frac{m}{s}$, meters/second, and metre/second represent the same unit in the Unit Converter.

You describe the options of the unit by using the optional arguments. The opts argument can contain one or more of the following equations.

'display'=string

This option gives the text that appears in the drop-down boxes in the Unit Converter dialog box.  If this option is not given, the entry is unit.

'default'=From, To, or a set of these

This option specifies whether the unit appears as the default unit in the From: or To: drop-down box when the corresponding dimension is selected in the Unit Converter dialog box.

'make'=truefalse

This option specifies whether the conversion tables are rebuilt after the unit has been added to the Unit Converter.  By default, this option is set to true. If $10$ or more dimensions or units are being added to or removed from the Unit Converter in the same execution group, it is recommended that you execute the Units[Converter][MakeConverter]() calling sequence afterward.

$\mathrm{with}\left(\mathrm{Units}\left[\mathrm{Converter}\right]\right)\:$

$\mathrm{AddUnit}\left(\frac{'\mathrm{parsec}'}{'\mathrm{year}\left[\mathrm{Julian}\right]'}\,'\mathrm{display}'=''parsecs\; per\; Julian\; year''\right)$

$\mathrm{AddUnit}\left(\frac{'\mathrm{cm}'}{'s'}\,'\mathrm{display}'=''centimetres\; per\; second''\right)$

$\mathrm{AddUnit}\left('\mathrm{kW}''h'\,'\mathrm{default}'='\mathrm{From}'\right)$