law: 11. Best judgment assessment.-
  If-
  (a) any person fails to make the return required by any notice given under sub-section (2) of section 8 and has not made a return or a revised return under sub-section (3) of that section, or
  (b) any person having made a return, fails to comply with all the terms of a notice issued under sub-section (1) of section 10, or
  (c) the Income-tax Officer is not satisfied about the correctness or the completeness of the accounts of the assessee, the Income-tax Officer, after taking into account all relevant material which he has gathered shall make the assessment of the chargeable receipts to the best of his judgment and determine the sum payable by the assessee or refundable to the assessee on the basis of such assessment.