The purpose of cost accounting is to provide management with pertinent cost measurements and analysis as a basis for managerial decisions. To fulfil this function the cost accountant has to adapt his thinking and methods to reflect the underlying economic conditions and abandon his stock-in-trade of conventional ideas. Two of the major faults of conventional accounting practice lie first in the failure to distinguish between fixed and variable costs and secondly in the unrealistic assumption, underlying much of the accountant’s work, that costs do not vary