The subjective transfer function (STF) approach is a method developed to evaluate Air Force command and control systems, and is applicable to other complex systems that are impossible to evaluate through traditional quantitative means. Based on the principles of hypothesis formulation and testing, the method incorporates features of the algebraic modeling approach to measurement where meaningful subjective scale values derive from tested theories. It also provides features for coalescing judgments obtained from different groups of system experts into an overall perceptual system outcome. This report introduces and is a primer of the STF method. It outlines the steps involved in the approach, describes how those steps can be accomplished, and discusses measurement principles and techniques to aid the reader's understanding of the basis for the approach.