The rules that use the vocabulary item "zero" are:

<hour-not_initial_zero>

zero

one zero

two zero

<bearing_number-pl>

zero <two_digits>

<hour>

zero

zero zero

zero one

zero two

zero three

zero four

zero five

zero six

zero seven

zero eight

zero nine

one zero

two zero

<bearing_number-three_dig-pl>

zero <two_digits>

<digit-pl>

zero

<digit_zero_to_five>

zero

<bearing_number-three_dig>

zero <two_digits>

<digit>

zero

<up_to_six>

zero

<bearing_number>

zero <two_digits>