Rectification of orders.

(1) The authority which made an assessment or passed an order on appeal or revision in repect thereof may, at any time within three years from the date of such assessment or order and of its own motion, rectify any mistake apparent from the records of the case, and shall, within the like period, rectify any such mistake as has been brought to its notice by a dealer : Provided that no such rectification shall be made having the effect of enhancing the assessment unless the authority concerned has given notice of its intention so to do and has allowed him a reasonable opportunity of being heard. (2) Where any such rectification has effect of reducing the assessment, a refund shall be due to the dealer. (3) Where any such rectification has effect of enhancing the assessment, a notice of demand shall be issued for the sum payable.