_The Necessity for measuring the Productive Powers of Capital Goods even in Primitive Life._--Now, it is necessary for every producer, though living in the simplest possible manner, to measure in some way the efficiency of the last unit of each kind of productive instrument that he uses. He has, let us say, a certain number of hatchets and of arrows, and he can produce one hatchet with the same amount of labor that would produce an arrow. Now, if a hatchet will do more good than an arrow, he will direct his energies to the making of the hatchet. It is important that any producer should bring the final units of the different parts of his equipment to a certain uniformity of producing power. He must not go on adding to the stock of implement No. 1 when implement No. 2, which could be had by the same expenditure of labor, would do more good; nor must he add to the stock of either of these after he has acquired such a supply of them that the first unit of implement No. 3 would be of greater importance. Measuring the efficiency of producers' goods is necessary in the case of every one who creates wealth at all, and such measurements reveal the fact that the more producers' goods of one kind a man has, the less is the productive power that resides in one of them.[5] [5] The law of diminishing returns of successive units of _capital goods_ is based on the same principle as the law of diminishing returns of _capital_, but it is not identical with it. We shall see, in due time, how a permanent fund of producers' wealth actually grows and why each new unit, as it adds itself to the fund, creates a smaller income than did its predecessor.