In operational modal analysis, the accuracy obtained in the identification of modal parameters, on the one hand, and the expertise in the modification of mass used to alter the dynamic behavior of the structure, on the other, decisively affect the accuracy achieved in the estimation of the scaling factors. Through experimental tests and numerical calculations, both the experimental validation of the estimate of the error in the scaling factor due to errors in the mode of vibration and the analysis of the influence of the modal mass in the variation of the scale factor, have been carried out. From all the above, it is concluded that it is necessary to pay special attention to how to make and modify inertial increments, i.e. changes in mass.