Example of SFH fitting and variability definitions for high-mass (log M_⋆/M_⊙ ≃ 10.2, left panel) and low-mass galaxies (log M_⋆/M_⊙ ≃ 8.5, right panel) in the SERRA simulation at z = 7.7. For each galaxy, we plot the star formation (SFR) in the upper panel as a function of cosmic time (t) and its fit (⟨SFR⟩, Eq. (1)) as a continuous and dashed line, respectively. We report the SFR starting from the time when the galaxy has a stellar mass higher than 10^6.5 M_⊙, the SFR is averaged in temporal bins of 2 Myr, and on the upper axis, we plot the redshift (z). In the lower left panel, we plot the variation (δ, Eq. (2)) as a function of time, add a constant line for no variation (δ = 0) to guide the eye, and report the p-value from the Kolmogorov–Smirnov test (p_KS) for the fit. In the lower right inset, we show the PDF of the variation, along with its Gaussian fit and standard deviation (σ_δ).