One of the more profound and complex differences between the three systems for scoring polygraph charts is the criterion established for the identification of the presence of physiological reaction and the identification of the lack of physiological reaction within each physiological tracing of each polygraph test question evaluated. This paper summarizes the primary criteria that each system uses in the interpretation of responses to control and relevant test questions. The systems are compared in the response areas of respiration, electrodermal activity, and cardiovascular activity. Differences among the systems are also noted for the assignment of numerical scores in each of the aforementioned physiological responses. The three systems are also compared in terms of the summation of scores. It is not the purpose of this paper to critically assess the features of each system with a view toward deciding which system is most objective in its scoring of polygraph charts. Rather the paper encourages familiarity with each system and further research in improving scientific objectivity in the interpretation of polygraph charts. Additional research into interpretation criteria and methods of comparison are especially needed. 1 table and 15 references