§ 19. Computation of net income. The net income shall be computed in
accordance with the method of accounting regularly employed in keeping
the books of such taxpayer; but if no such method of accounting has been
so employed, or if the method employed does not clearly reflect the
income, the computation shall be made upon such basis and in such manner
as in the opinion of the director of finance does clearly reflect the
income. In determining net income, war losses, taxation of property
recovered, and basis of property shall be treated in substantially the
same manner as such losses, recoveries and basis are treated under the
applicable provisions of section thirteen hundred thirty-one of the
internal revenue code.