Computation of undisclosed income: block period aggregation and exclusions govern assessment based on search and requisition evidence. The total undisclosed income of the block period is the aggregate of undisclosed income declared in the special return and undisclosed income determined by the assessing officer from search, survey or requisition evidence, subject to specified exclusions such as incomes already assessed or declared prior to search, income computed from books maintained in the normal course for periods surrounding the search, and certain statutory categories; income from international or specified domestic transactions within the narrowly defined authorisation period is excluded from block computation and governed by other assessment provisions.