Assuming that the Trust is planning a new business and determining the most profitable output, it will limit that output not necessarily at the point where the selling price gives the widest margin of profit upon the expenses of production, as might be the case at the point B in the diagram, but at the point F, where the margin of profit bears the largest proportion to the expenses of production, or in other words, where the area of absolute takings shows the largest surplus over the area of aggregate expenses. Thus it will here be to the interest of the Trust to produce and sell six millions (limiting production at F) with an aggregate expense AFF'A' and an aggregate takings AF_fa_, yielding an aggregate net profit A'F'_fa_. They will not produce five millions because the figure AE_ea_ bears a smaller proportion to AEE'A' than does AF_fa'_ to AFF'A'. For a similar reason they will not produce seven millions. Since the fluctuations in the curve of expenses and in that of selling price or "demand" are determined by an entirely different set of forces, it will be evident that there may be several points in AL where the proportions between the area of expenses and that of profits may be the same. So there may be several maxima at which Trust prices may be indifferently fixed. The figure upon F'_f_ may have the same quantitative relation to the figure upon FF', as that upon H'_h_ to that upon HH'. In such a case it will be a matter of indifference to the Trust whether it sells five million tons at a price 100s. per ton, or seven millions at 90s. We have seen that the causes which determine expenses at the several points in A'L' have no relation to the causes which determine the selling price at the various points, except to furnish a minimum below which the price cannot fall. Above this limit expenses of production in no sense help to determine monopoly prices; the true determinants are entirely in the region of demand, and are measured by the marginal utility or satisfaction afforded to consumers by the several quantities which constitute supply at any given time.