The UsingSystem() function returns the current default system of units.

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

Automatically loading the Units[Simple] subpackage

$\mathrm{UsingSystem}\left(\right)$

$\mathrm{SI}$

$\mathrm{UseSystem}\left('\mathrm{CGS}'\right)$

$\mathrm{UsingSystem}\left(\right)$

$\mathrm{CGS}$