THE REQUIREMENTS imposed by an advanced or single specimen procedure have been enumerated in previous sections. If a carefully aligned load train is combined with a proper set of clevises and a well-machined specimen, most of the problems associated with single specimen compliance tests will not be observed. If a d-c electric potential system is used, a crack opening displacement transducer signal quality corresponding to the basic test procedure is fully adequate. A test system schematic for an unloading compliance test system is shown in Fig. 34, while the additions required for an electric potential system are shown in Fig. 35.