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

<degree_setting-not_digit_sequence-180>

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

<degree_setting-not_digit_sequence-not_initial_zero-90>

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

<degree_setting-digit_sequence-180>

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