The general purpose of psychological tests is to determine how individuals compare with one another in mental capacity, or with standards based upon the capacities of individuals known to possess certain qualities. Thus, it may be desirable, as it frequently is, to determine the relative abilities of the individuals of a certain group, like a school or college class, clerks employed in a similar form of work, a number of applicants for a certain position for which only the most capable among the candidates is desired, or the soldiers of a particular company or regiment. What is required here is a method of grading these individuals with reference to one another, by means of tests which need not necessarily have any relation to any external standard of mental perfection. The process here is as if one were to be told to pick out of all the automobiles in a garage the best one, the next best, and so on, classifying these particular cars and no others _with relation to one another_ and not with respect to any standards of automobile perfection introduced from outside. None of the cars might be perfect; perhaps the best one of the lot has leaky piston-rings and none of them will climb a 10 per cent. grade on high gear. It is a comparatively easy matter, however, to devise a few simple tests that will grade a dozen or fifty automobiles in regard to their relative ability to climb hills, carry loads, and perform the other services expected of an automobile. The one that will climb hills the best may not also be the one that will carry the heaviest load or travel the most miles on a gallon of gasolene, but out of such a series of group tests any one interested can readily determine which of all the automobiles in the group is the best general purpose car, which the poorest, and about where the others grade with reference to these two extremes. That is about the process that a man engaged in the automobile trucking business would use in determining which one of the cars he has available is best adapted for a particular piece of hauling that is to be done. He wants to know which of his cars he can rely upon for any one of many different sorts of service, but he particularly wants to know all the time which of them are worth spending money on for repairs and improvements and general overhauling and which are either so poorly constructed in the first place or so hopelessly out of repair that it is cheaper to scrap them than to spend any more money on trying to make them fit for service. _In other words, the automobile owner needs to know which of his cars, however poor its present ability, has such inherent qualities as to justify the belief that it can be made more efficient by proper attention and reasonable expenditure of money._