Using a comparative study in the area of sciences is universal and has a long tradition. However, separate comparative disciplines are not created at a wide scale. Usefulness of applying the comparative study method is one among many of ways of examining the reality. It is useful on account of the great diversity of the structure of agricultural engineering objects and processes associated with them, which can be easily analyzed with the use of the comparative study. In the agricultural engineering it is possible to compare things and processes at the stage of the design, the structure and the use of agricultural machines, as well as to compare other processes occurring in the area of the technique. The study was conducted on the example of the information obtained through computerized diagnostic tests used in the diagnosis of farm tractors and the selected processes of planned maintenance service review.