Comparison of solar magnetic fields observed with various telescopes and/or in different spectral lines is important to verify the data reliability from instrumental points of view, and to determine some physical processes responsible for the origin of polarized emission in the solar atmosphere with extremely complicated distribution of magnetic and thermodynamic parameters in an aperture of observation and along the line-of-sight. When compared observations use the same line, and data reveal a significant systematic discrepancies, the question arises about the reasons of that. If compared data are obtained in different spectral lines, the existence of differences between them could be related to peculiarities of the polarized emission formation in one or another line. In this case the question arises - data in which line are more reliable? This problem is especially acute with regard to observations in the FeI $\lambda$525.02 nm spectral line due to the big Lande factor ($g = 3.0$) and low excitational potentional of this line. Recently this problem has become especially urgent for some space weather tasks. Both the analysis of this problem and main bibliographic references can be found in [1].To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html