Income tax rates and surcharges set by First Schedule determine tax, withholding and advance tax computation rules. Income-tax for assessment year beginning 1 April 1973 is charged at rates in Part I of the First Schedule with applicable surcharges; companies with life insurance profits compute tax by aggregating tax at the Life Insurance Corporation rate on such profits and tax at the company rate on remaining income. Withholding is at rates in Part II. Income-tax and advance tax in the specified cases follow Part III procedures and rates, with special aggregation rules for net agricultural income and defined terms for company types, insurance commission, net agricultural income and tax-free securities.