Notice of scrutiny requires timely service; noncompliance can permit ex parte assessment and attract penalty. A notice for scrutiny must be served on the assessee to require attendance or production of evidence within the prescribed limitation period measured from the end of the financial year in which the return was furnished; judicial decisions govern validity where revised returns are filed or notices affixed after hours. Where the assessee has cooperated in proceedings, service may be deemed; failure to comply can lead to ex parte best judgment assessment and penalty. For institutions and trusts, alleged specified violations require the AO to refer the matter to the Principal Commissioner or Commissioner and assessment time limits exclude the period between reference and receipt of the Commissioner's order.