The paper presents the method of rationalization of diagnostic test of machines, using the level of informative entropy about their technical state. According to the theory of information, the larger the differentiation of the probabilities of damage of individual parts of a machine, the smaller the informative entropy. In such a case we need less information from diagnostic tests to qualify the technical state of machine. This fact was used in differentiating the probabilities of damage of parts based on information about their exploitation. A suitable order of checks was proposed, which allows an essential decrease of the expenditures of diagnostic tests of machines.

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