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It is shown that the most important component of scientific research is the experiment. One of the most important purposes of its conduct is the verification of theoretical provisions (confirmation of the working hypothesis). It has been proven that together with perfect measuring tools, rational methods of conducting tests and processing the obtained results should be used. It was noted that when indicating the ICE, it is important to take into account the peculiarities of the course of rapidly changing and non-stationary processes in the ICE: high rates of change of processes, wide frequency spectrum, nonidentity of the course of processes from cycle to cycle. This determines the specific requirements of the methodical plan and to the measuring devices themselves in terms of speed, frequency of recording, and the rationality of the methods of conducting experimental research. It has been proven that when researching engines, it is necessary to have both single-cycle indicator diagrams and an averaged, over several hundred, indicator diagram. It is shown that when registering the pressure ordinates of the indicator diagram, it is necessary to have a scientifically based method of their measurements. The general features of the experiment when obtaining the indicator diagram are determined, which ensure the desired accuracy and reliability of its receipt. It is shown that the purpose of the work is to experimentally verify the performance of the improved method of choosing the discretization step and choosing the number of registered ordinates of the indicator diagram of the ICE in one working cycle, depending on the approximation error and the pressure build-up rate. The general method of determining the frequency of discretization of indicator diagrams depending on the required accuracy of its approximation and the improved expression for its determination are presented. The scheme for determining the sampling frequency by the angle of rotation of the crankshaft is presented. The essence of the improved method of choosing the discretization step of the indicator diagram is considered, by dividing it into zones and choosing different discretization steps in each zone. The use of a digital microprocessor complex for the study of working processes of a specific diesel engine is considered. The initial data and the results of the calculations of the discretization angles, necessary for conducting the experiment, were determined. Options for changing the discretization step are considered. The validity of the given expressions for the indicator diagram with a smoothed polytrope is proved. The scheme for determining the error of restoration of the indicator diagram by the method of piecewise linear approximation is given. Approximation errors were calculated based on experimental data, which confirmed the correctness and acceptability of both the proposed expression for finding the necessary discretization step and the proposed method of obtaining indicator diagrams using digital methods and means of controlling the parameters of the internal combustion engine. [ABSTRACT FROM AUTHOR]