... SHTOL ' Special Astrophysical Observatory of the Russian AS, Nizhnij Arkhyz 357147, Russia The investigation of such a phenomenon as the magnetic field variability at long times (years - decennials) is very interesting. If the explanation of the magnetic field variability with rotation period by the oblique rotator model is evident, then the reason of the long-period variability is not clear yet, despite the existence of some assumptions on its nature. ... Fig.2. ... 213 Fig.3. ...