(1) Use of the completed contract method of accounting for long-term contracts requires that income derived from sources within this state from incomplete contracts in progress outside this state on the date of withdrawal, dissolution or cessation of business in this state be included in the measure of tax for the taxable year during which the corporation withdraws, dissolves or ceases doing business in this state.

(2) The amount of income (or loss) from each such contract to be apportioned to this state by the apportionment method set forth in ARM 42.26.904 shall be determined as if the percentage of completion method of accounting were used for all such contracts on the date of withdrawal, dissolution, or cessation of business. The amount of apportionable income (or loss) for each such contract shall be the amount by which the gross contract price from each such contract which corresponds to the percentage of the entire contract which has been completed from the commencement thereof to the date of withdrawal, dissolution, or cessation of business exceeds all expenditures made during such period in connection with each such contract. In so doing account must be taken of the material and supplies on hand at the beginning and end of the income year for use in each such contract.