The category "<unit>" can be expressed as follows:

<unit>

<det-not_indef-pl> <unit_nom-not_det-pl>

<det-not_indef-sing> <unit_nom-not_det-sing>

<full_unit_call_sign>

<full_unit_call_sign> and <full_unit_call_sign>

<track_designation>

<unit_nom>