I. Various criteria and their evaluation, 561; rate-of-turnover criterion, 561; social marginal productivity criterion, 562; reinvestment criterion, 564; an alternative, time series criterion, 568. — II. Application of these criteria to some models, 571; the first model, on the contrast between the criteria; the importance of labor cost, 571; the second model, on the foreign exchange consideration, 577; the third model, on the choice involving time, 582.