Haw. Rev. Stat. § 239-8: Allocation and apportionment.

(a) The gross income included in the measure of the tax, as defined in paragraphs (2) and (3) of the definition of "gross income" in section 239-2, shall be determined by an allocation and separate accounting so far as practicable.

(b) If under paragraph (2) of the definition of "gross income" in section 239-2, an apportionment of gross income is necessary, there shall be apportioned to the State and included in the measure of the tax that proportion of the total gross income, so requiring apportionment, that the direct cost of the transportation, conveyance, or transmission designated in paragraph (2) of the definition of "gross income" in section 239-2, bears to the total direct cost of the transportation, conveyance, or transmission the gross income from which requires apportionment.

(c) If under paragraph (3) of the definition of "gross income" in section 239-2, an apportionment of gross income is necessary, there shall be apportioned to the State and included in the measure of the tax that proportion of the total gross income, so requiring apportionment, that the total direct cost of the transportation, conveyance, or transmission within the State bears to the total direct cost of the transportation, conveyance, or transmission the gross income from which requires apportionment.