4Each report made by the Corporation under section 6(2) of this Act after they are required to make a determination in pursuance of paragraph 2 or 3 above shall contain a statement of the method or, if more than one method is used, of each method, by which turnover is determined by the Corporation for the purposes of that paragraph ; and, in any such report containing a statement made in pursuance of either of those paragraphs, there shall be stated with respect to each matter involving a determination by the Corporation (other than the determination of an amount of turnover) the method by which that determination is arrived at.