The modern instalment credit sale may be justly compared to an intricate piece of machinery. Its legal structure is composed in part of legal rules, in part of contractual provisions. But a study of the machine's design will not suffice to reveal its everyday operation, for legal devices contain many tools intended only for emergency use. For an understanding of the operation of the mechanism which has been created for instalment sale credit, it is necessary to examine it with reference to the business practices which have developed in its employment. This article, accordingly, seeks to depict not only the legal structure of the instalment credit sale but also its operation, chiefly as it is revealed in the retail sale of automobiles.' The diversity in both the fields of law and practice2 is such that generalization has been compelled, with the consequent sacrifice of those qualifications essential to complete accuracy. Detailed portrayal, however, would require a corpulent treatise. Instalment selling in the average retail sale where the seller himself assumes the burden of carrying the credit is characterized by relatively simple agreements3 usually