XXIII MEASURING BY LIMITED IMPRESSIONS The method of determining correlations described can be applied, with slight adaptations, to many industries where large-scale production is carried on. The future will see an even greater division of labor and refinement in manufacturing methods; consequently, the method of comparative productiveness will be applicable to an ever increasing extent. Still there will always be instances where relative productiveness can not be computed mathematically, ­ and where the process of production will not meet the three conditions outlined. The following instances ­ may be given as representative of conditions under ­ which the method of comparative productiveness is not applicable: 1. The small factory, in which the variety of work to be done is large in proportion to the number of workers employed. ­ Each employee is likely to be engaged in several different operations each day, making it impossible to compare individuals on the basis of identical work done under identical conditions. 2. Offices, in which the variety of work is almost infinite, and in which it is practically impossible to compute ­ the relative productiveness of individuals. 3. Service corporations such as railroads, street-car companies, etc., where the conditions of service vary greatly, and where, in consequence, it is difficult to compute ­ exactly the relative usefulness of individuals. 320