Provided that the tax shall be charged at the rate at which it would have been charged if such income had not escaped assessment or full assessment as the case may be.

Rectification of mistake Rectification of mistake.--(1) Any authority which passed an order of assessment or any order in appeal or revision may, on his own motion, or on an application by the assessee, at any time within three years from the date of such order, rectify any mistake apparent on the face of the record of the assessment, appeal or revision, as the case may be : Provided that no such rectification shall, if it has the effect of enhancing the assessment, be made unless the assessee has been given reasonable opportunity of being heard.

1. (2) Where any such rectification has the effect of reducing the assessment, the assessing authority shall refund the excess amount to the assessee.