Assessment powers: Assessing Officer may demand documents, inquire into foreign assets and make best judgment assessments. Section 10 empowers the Assessing Officer to require production of accounts or documents and to make inquiries for assessing undisclosed foreign income and assets; after considering evidence he must assess or reassess and determine sums payable, and where a person fails to comply with notice requirements the Assessing Officer may, after considering available material and giving an opportunity of being heard, make a best judgment assessment.