Assessment amendment power permits reassessment to include or correct omitted partnership and association income within prescribed period. The provision empowers the Assessing Officer to amend completed assessments to include or correct a partner's or member's share when it is found omitted or incorrect, and to recompute total income where allowances, deductions or capital gain computations previously made are later determined to be wrongly allowed or revised; such amendments follow rectification procedure rules and are subject to expressly prescribed limitation periods reckoned from specified triggering events.