Commonwealth Electoral Act 1918

In a House of Representatives election a person shall mark his or her vote on the ballot paper by:

writing the number 1 in the square opposite the name of the candidate for whom the person votes as his or her first preference; and

writing the numbers 2, 3, 4 (and so on, as the case requires) in the squares opposite the names of all the remaining candidates so as to indicate the order of the person’s preference for them.

The numbers referred to in paragraph (1)(b) are to be consecutive numbers, without the repetition of any number.