THE measurement of outputs of agricultural systems and their valuation are always a complex proceeding, and the results of any methods of measurement and valuation which have been used up to the present time are to some extent indefinite. Outputs vary in their physical and biochemical characteristics, and in their human uses and values. The only common measure of outputs of varied characters is their money value at any given time. Relative prices of one product and another vary from time to time, and therefore the values of outputs of given quantities of products also vary. A system or type of farming which may be shown to be efficient at one period may prove to be relatively inefficient a short time later, due solely to changes which have occurred in markets.