An Act amending the "Tax Reform Code of 1971" approved March 4, 1971 (P. L. 6, No. 2), further providing for exclusions from sales tax, for a minimum tax for capital stock and foreign franchise tax purposes, for an election in computing franchise tax and for the calculation of tax when tax rates are changed during a tax year; providing for the tax treatment of Pennsylvania S corporations and their shareholders; defining the phrase "installment sales method of reporting"; and further defining "sales" for the purpose of apportionment of income and, in certain cases, apportionment of capital stock value.