161 9. (a) All costs, expenditures, proceeds and revenues and all determinations of price and value referred to in this article shall be the result of free market or arm's length transactions. In the absence thereof, they shall be determined by the Authority, after consulting the contractor, as though they were the result of free market or arm's length transactions, taking into account relevant transactions in other markets. (b) In order to ensure compliance with and enforcement of the provisions of this paragraph, the Authority shall be guided by the principles adopted for, and the interpretation given to, arm's length transactions by the Commission on Transnational Corporations of the United Nations, the Group of Experts on Tax Treaties between Developing and Developed Countries and other international organizations, and shall, in its rules, regulations and procedures, specify uniform and internationally acceptable accounting rules and procedures, and the means of selection by the contractor of certified independent accountants acceptable to the Authority for the purpose of carrying out auditing in compliance with those rules, regulations and procedures. 10. The contractor shall make available to the accountants, in accordance with the financial rules, regulations and procedures of the Authority, such financial data as are required to determine compliance with this article. 11. All costs, expenditures, proceeds and revenues, and all prices and values referred to in this article, shall be determined in accordance with generally recognized accounting principles and the financial rules, regulations and procedures of the Authority. 12. Payments to the Authority under paragraphs 5 and 6 shall be made in freely usable currencies or currencies which are freely available and effectively usable on the major foreign exchange markets or, at the contractor's option, in the equivalents of processed metals at market value. The market value shall be determined in accordance with paragraph 5(b). The freely usable currencies and currencies which are freely available and effectively usable on the major foreign exchange markets shall be defined in the rules, regulations and procedures of the Authority in accordance with prevailing international monetary practice. 13. All financial obligations of the contractor to the Authority, as well as all his fees, costs, expenditures, proceeds and revenues referred to in this article, shall be adjusted by expressing them in constant terms relative to a base year. 14. The Authority may, taking into account any recommendations of the Economic Planning Commission and the Legal and Technical Commission, adopt rules, regulations and procedures that provide for incentives, on a uniform and non-discriminatory basis, to contractors to further the objectives set out in paragraph 1. 15. In the event of a dispute between the Authority and a contractor over the interpretation or application of the financial terms of a contract, either party may submit the dispute to binding commercial arbitration, unless both parties agree to settle the dispute by other means, in accordance with article 188, paragraph 2.