Time evolution of flux emergence and chromospheric emission: The unsigned latitudinal and longitudinal average of the azimuthal surface magnetic field, ⟨B_ϕ⟩_(ϕ, θ), is shown in blue and green points indicating where the signed average is negative or positive, respectively. The solid curves are single sinusoidal fits to ⟨B_ϕ⟩_(ϕ, θ) in the case of the Sun and 61 Cygni A, and a fit using a sum of two sinusoids for ϵ Eridani. The light blue bars indicate the estimated error bars for ⟨B_ϕ⟩_(ϕ, θ), as described in the text. The independently determined level of chromospheric activity as measured by the S-index is shown with red points and the vertical bar at year 2020 shows the S-index error bar. Top row: Sun at high resolution; Second row: Sun at the equivalent resolution of the ZDI maps; Third and fourth rows: results for 61 Cygni A and ϵ Eridani, respectively. Left panel: extends back to the S-index observations obtained in the 1960s while the right-hand panel zooms into the time period where there are also magnetic maps.