Method of accounting: permits cash or mercantile systems, allows notified accounting standards and AO assessment under section 144. Substitution of section 145 prescribes that income under business/profession or other sources shall be computed in accordance with either the cash system or the mercantile system of accounting regularly employed by the assessee; the Central Government may notify accounting standards for classes of assessees or income; and where the Assessing Officer is not satisfied about account correctness/completeness or regular adherence to the method or standards, the Assessing Officer may make an assessment in the manner provided by the assessment provision.