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Published online by Cambridge University Press: 25 May 2016
This brief review presents the current state of observations of stellar activity effects including the fluxes of chromospheric emission lines: CaII H+K, MgII h+k, SiII 1812 Å multiplet, CIV, as well as radio and X-ray fluxes versus B-V colours and luminosity classes, rotation periods, Rossby number and especially versus the mean magnetic flux density 〈fB〉. Results of stellar magnetic field measurements are presented.