We have discovered two reasons why the effective utility of any one of the earlier units is equal to the absolute utility of the final one. The first reason is that, if any one of them were lost, the final one would be put in the place of it and the consumer would suffer no loss except what would be entailed by going without the last unit. The second reason is that if the consumer should lose any one of the earlier units, he could replace it by the same amount of labor that would replace the final one. We have seen that the line _DC_ of the figure expresses not only the absolute utility of the final unit of goods, but the disutility of the labor of reproducing it or of reproducing any other unit. The cost of replacing the whole supply is expressed by the area _AECD_, on the supposition that the units are replaced, one at a time, by means of labor performed at the end of several working days when the sacrifice is greatest. Total value is thus quantitatively equivalent to total _effective sacrifice of replacement_, as well as to total effective utility. If, by adding a brief period to the length of one working day, a man can make good the loss of one unit of the goods, by adding the same period to the length of a number of working days, he can make good the loss of the total supply. For simplicity we assume that the man's physical condition remains unchanged, and that an extra hour of labor at the end of any one day costs him as much as it would at the end of any other. _How Primitive Man measures the Productivity of Labor and Capital._--There is a truth relating to producers' wealth that resembles the truth that we have just stated with regard to consumers' wealth. The more consumers' goods of one kind a man has, the less is the value that any one of them has to him. The more producers' goods of a given kind a man has, the less is the efficiency that any particular one of them possesses as an aid to labor. The last bit of bread serves the man himself in a less important way than does the first, inasmuch as it gratifies a want that is less intense; and the last implement of a given kind--the last hatchet or spade or arrow--helps him less in his productive operations than did the first one. On the one hand, we have the law of the diminishing utility of successive units of consumers' goods, and on the other hand, we have a parallel law of the diminishing productivity of successive increments of producers' goods.