Results of investigation of influence of tilt of mirror surface on the measurement accuracy of laser triangulation rangefinder are represented. Optical system of sensor satisfying to Scheimpflug's principle is considered. The measuring errors produced by asymmetry of light distribution in photorecording plane at sensing a surface by anisotropic Gaussian light beam are analyzed. The example of measuring a melt level in the crucible during the Czochralski pulling is considered at which the tilt of a melt surface depends on angular velocity of crucible rotation.