Time series of the ⟨ B_z ⟩ values obtained for β CMa (top panels) and ϵ CMa (bottom panels) using a line mask that includes (left panels) or excludes (right panels) helium lines. The black asterisks show the ⟨ B_z ⟩ values derived from the observations carried out in December 2013. The red rhombs show the ⟨ B_z ⟩ values obtained from each consecutive observation carried out in April 2014. The blue triangles indicate the ⟨ B_z ⟩ value extracted from the average LSD profiles obtained on 21 April 2014. The green dot on the left side of the top left panel shows the ⟨ B_z ⟩ value obtained by Silvester et al. (2009, S09) from the ESPaDOnS observation of β CMa carried out in 2008.