Rectification of advance ruling permits correction of apparent errors, with hearing required before increasing tax or cutting input credit. Authority or Appellate Authority may amend orders under the advance ruling provisions to rectify any error apparent on the face of the record within six months of the order, on its own motion or on notice from officers or parties; however, any rectification that would enhance tax liability or reduce admissible input tax credit requires that the applicant or appellant be given an opportunity of being heard.