Amplitude and frequency variations in f₂ and its partner pulsation mode (−f₀ + 2f₁) for the five HADS. $\mathrm{\Delta }A/\overline{A}$ is highlighted in red, which represents the relative amplitude variations. Δf is highlighted in blue, which represents the absolute frequency variations. ρ_A, f is highlighted in green, which represents a perfect correlation or anti-correlation between the variations in the amplitude and frequency when it equals +1 or –1, respectively.