Top panel: empirical cumulative distribution function of the ⟨ F_HK ⟩ measurement for young (solid line) and old (dashed line) stars, following the classification of Maldonado et al. (2017) based on kinematics. Central panel: standard deviation of the H&K measurements corrected for the quadratic trend (Sect. 4.2) as a function of the average level of activity ⟨ F_HK ⟩. The black dashes represent the best-fit line; the best-fit coefficients are given in Table 2. Filled and open circles mark young and old stars, respectively. Bottom panel: same as in the middle panel, but for the residual Hα line.