Automation of the investigation system of evolution of the technical system condition (machines) in which diagnosing distinguishes itself from condition prognosing and genesis requires qualifications to gather diagnostic parameters describing the change of machine condition during exploitation. The notion used above joins with suitable criteria and investigation of these problems in the search for the solution. The achievement of this aim requires studying the methodology of reduction of diagnostic parameter gathering, including optimization and performance of the solution pattern. The implementation of settlements and proposals included in the study should enlarge the effectiveness and efficiency of diagnosing machines, and at the same time contribute to rationalizing their exploitation. The results of investigations connected with the implementation of procedures of monitoring the technical condition of machine engines and the investigation of chosen arrangements of mechanical vehicles were introduced. Examples of the rule of diagnostic inference were presented for the gathering of diagnostic parameters and opinion on the condition.