In this paper, the author proposed a new method for determination of vertical displacements with the use of hydrostatic levelling systems. The traditional method of hydrostatic levelling uses a rule in which a position of reference sensor is stable. This assumption was not adapted in the proposed method. Regarding the issue mentioned above, the reference sensor is treated in the same way as the others sensors that measure the liquid level. As a consequence of this approach there is a possibility of vertical displacement determination of both the reference sensor as well as the remaining controlled sensors. A theoretical considerations were supplemented with the practical examples. The possibility of calculating the vertical displacement of reference sensor is an undoubted advantage of the submitted proposal. This information enables more detailed interpretation of the vertical displacements results obtained from hydrostatic levelling systems. Thus, wider knowledge about maintenance of the entire examined object treated as the rigid body is obtained. The tests that were carried out confirm the theoretical assumptions and encourage to perform further, more precise empirical analyses.