Long fluid level tilt meter has been developed since 1965 at FGI for studies of tidal deformations of the earth crust, internal structure of the earth and Fennoscandian postglacial rebound (PGR). Institute have built and carried out measurements with NS (63m) and EW (177 m) long water level tilt meters at Tytyri mine in Lohja in 1977–1998. New technical details of the instrument and new computer controlled recording interferometer have been developed since 2000 and one version of the instrument is in test phase in our laboratory. By improving the interferometrical accuracy of tilt meter, we try to get new information from e.g. earth internal structure, crustal tilting because of PGR and many related phenomena.