Safe harbour for diamond mining income: eligible raw-diamond sales accepted at a prescribed margin, streamlining tax treatment and compliance. The rules create a safe harbour for foreign companies engaged in diamond mining selling raw diamonds in notified special zones: an eligible assessee opting in must declare income meeting a prescribed profit margin relative to gross receipts. If the option is valid, deductions under routine business expense and depreciation provisions are treated as given, written down value is adjusted accordingly, and set off of unabsorbed depreciation and carried forward losses or losses from other businesses is disallowed. Form No. 3CEFC must be filed to opt in; the assessing officer may invalidate the option for incorrect or concealed facts, and mutual agreement procedure is barred for the eligible business.