810. Apportionments.

For the purposes of computing a gain or loss, any necessary apportionment must be made of any consideration or of any expenditure, and the method of apportionment adopted must be just and reasonable1. Where the apportionment of any amount or value may affect the capital gains tax liability for any period of two or more persons, whether for the same or different periods, and it is not or has not been a material question in an appeal already brought by any of them, any of them may apply to the tribunal to determine the mode of apportionment