Presumptive taxation for specified professions governs income computation, deductions, audit duties, and advance tax obligations. Special provision for computing profits and gains of a specified profession on a presumptive basis applies to eligible resident assessees carrying on notified professional activities. The presumptive income is the higher of 50% of gross receipts or the profit actually claimed, subject to the prescribed turnover limit, with a higher limit where cash receipts do not exceed 5% of total receipts. The provision overrides contrary computation rules, restricts additional deductions and loss claims, and applies books, audit, written down value, and advance tax requirements in specified cases.