This paper presents the possibilities of the processing of indicator diagrams by means of the moving approximation objectsdeveloped by the author, which are based on the least squares method. The rules of creating the approximating objects withthe use of the spline knots have been discussed: glued, riveted and broken knots as well as multiple approximation. Byusing the example of the processing of indicator diagrams of the medium-speed marine engine, the quality of the mileageapproximation for a few types of the approximating objects has been compared. Some examples of curve smoothing and determining of derivatives and separating the high-frequency noise and disturbances caused by gas channels have beenpresented as well.