Top panel: comparison between the measured amplitude A₈ of f₈ and 60 × A_{1, −}·A₄ (where A_{1, −} and A₄ are the amplitudes of f_{1, −} and f₄, respectively) at each time segment (see text). Bottom panel: same as top panel but for a comparison between the measured frequency f₈ and sum of the frequencies f_{1, −} + f₄. In both cases, the relationship is exactly statisfied along the plain diagonal line. All the measurements are found to be within 2σ of this line.