The paper concerns instruments used in the determination of task performance efficiency of mechanical and electronic maintenance men. Composite results of unvalidated knowledge tests, theory tests, school marks, and supervisors' ratings are presented which indicate that these measurement instruments have low empirical validity. The limitations of traditional systems effectiveness measures are also discussed. Although job task performance tests (JTPT) have higher empirical validity, they have had limited use due to their relatively high cost factors. A series of efforts to develop better criterion referenced JTPT, and to attempt the development of paper and pencil symbolic substitute tests of high empirical validity, were made. Described is the model battery of 48 criterion referenced JTPT covering all key maintenance activities (checkout, align/adjust, remove/replace, troubleshooting, test equipment, and soldering), intended for use on the job, in training, and for validation of symbolic substitute tests. Developed batteries of graphic and video symbolic substitute tests were given limited validations. Suggestions are made for use of the criterion referenced JTPT in improving maintenance efficiency. Fourteen references are listed, and an appended section describes limitations of system effectiveness measures. (Author/MS)