The rules that use the category "<degree_unit-sing>" are:

<degree_setting-not_initial_zero-90>

<degree_number-not_initial_zero-90-sing> <degree_unit-sing>

<degree_setting-180>

<degree_number-180-sing> <degree_unit-sing>

<degree_setting-360>

<degree_number-360-sing> <degree_unit-sing>