The rules that use the category "<digit>" are:

<controller-air_traffic_control-recursive>

<call_sign_controller> <digit> <digit>

<air_speed_number>

<digit-not_zero> <digit> <digit>

<reference_point>

<point_type-bullseye-sing> <digit>

<second_setting>

<minutes-pl> point <digit> <digit> <time_interval_unit-second-pl>

<minutes-sing> point <digit> <digit> <time_interval_unit-second-sing>

<degree_number-not_initial_zero-90-pl>

<digit_one_to_eight> <digit>

<bomb_damage_description>

<digit> of <target_description-pl> <damage_descriptor>

<bearing_number-pl>

three <up_to_six> <digit>

<up_to_two_digits-sing>

<digit> <digit-sing>

<degree_number-180-pl>

<digit> <digit>

<digit-0> <digit_not_one> <digit>

<digit-0-pl> <digit-1> <digit>

<digit-1> <digit_zero_to_seven> <digit>

oh_one <digit>

<up_to_two_digits-pl>

<digit> <digit-pl>

<degree_number-180-digit_sequence>

<digit> <digit>

<digit-0> <digit_not_one> <digit>

<digit-0-pl> <digit-1> <digit>

<digit-1> <digit_zero_to_seven> <digit>

oh_one <digit>

<up_to_two_digits>

<digit> <digit>

<bearing_number-three_dig-pl>

three <up_to_six> <digit>

<up_to_four_digits>

<digit> thousand

<unit_call_sign>

<air_call_sign_prefix-takes_digit> <digit>

battalion <digit-not_zero> <digit>

battalion <digit-not_zero> <digit> <digit>

battalion <digit-not_zero> <digit> <digit> <digit>

<battle_position>

<battle_position_noun> <digit> <digit> <digit>

<minutes>

<digit_zero_to_five> <digit>

<air_call_sign_prefix-takes_digit>

<air_call_sign_prefix-not_takes_digit> <digit>

<controller-air_traffic_control>

<call_sign_controller> <digit> <digit>

<tens_number-pl>

<digit-not_zero> <digit>

<bearing_number-three_dig>

three <up_to_six> <digit>

<altitude>

<altitude_unit> <digit> <decimal>

<decimal>

point <digit>

<controller>

<call_sign_controller> <digit> <digit>

<number>

<digit> <digit>

<tens_number>

<digit-not_zero> <digit>

<number-pl>

<digit> <digit>

<loadable_item_callsign>

pallet <digit> <digit> <digit>

<minutes-pl>

<digit_zero_to_five> <digit>

<bearing_number>

three <up_to_six> <digit>

<controller-recursive>

<call_sign_controller> <digit> <digit>

<coordinate_nums>

<digit> <digit> <digit> <digit>

<digit> <digit> <digit> <digit> <digit> <digit>

<digit> <digit> <digit> <digit> <digit> <digit> <digit> <digit>

<air_call_sign_prefix>

<air_call_sign_prefix-not_takes_digit> <digit>

<two_digits>

<digit> <digit>

<minutes-sing>

<digit_zero_to_five> <digit>