Successful prediction of judicial decisions is inherent in a true "rule of law." It is also a dream of many a law student and a nightmare to the culture complex of legal and juridical professions. The author, of the Pennsylvania State University Department of Political Science, takes us step by step through a hypothetical set of cases. Using well-known arithmetical and algebraic operations, he follows key variables from prior cases to determine the likelihood of judgment for a litigant in a new case.