Telegraphic transfer buying rate governs conversion of foreign currency income for tax computations, replacing prior exchange instruction. The conversion of foreign currency incomes for tax purposes must use the telegraphic transfer buying rate adopted by the State Bank of India on the specified date in the amended rule; the amendment applies to incomes accruing, arising or received on or after the rule's operative date, while pre-amendment rates apply to earlier incomes. The earlier administrative instruction is modified where inconsistent with the rule, and reopening of assessments may be undertaken where rectification is unavailable.