Where a registered dealer makes a, sale of any goods, other than those specified in Part B of Schedule IV, or containers or other materials, to a registered dealer for use directly by such registered dealer in the manufacture of any other goods in his industrial unit situated in a Special Economic zone or for the packing of goods purchased or goods to be manufactured by such registered dealer in such industrial unit, the dealer selling such goods or containers or other packing materials may, for the purpose of determining his taxable turnover of sales, deduct under sub-clause (xi) of clause (a) of sub-section (3) of Section 17 from his gross turnover of sales that part of such gross turnover of sales which represents the sale to such registered dealer for the purpose as aforesaid in such industrial unit:

Provided that the claim for deduction shall not be allowed unless the dealer selling the goods furnishes, on demand, before the appropriate assessing authority a certificate in Form 10, duly filled in and signed by the registered dealer to whom such goods are sold, to the effect that the goods, containers and other packing materials purchased by him are covered by the letter of authority issued in his favour by the Development Commissioner of the Special Economic Zone of any officer authorised by him