O − C analysis of GSN 069 under two global cycle assignments. Left: reference assignment with N_{FinalEpochStart} = 426. From top to bottom, the panels show the O − C values relative to the fixed linear ephemeris, the baseline-subtracted modulation ﹩{\rm{\Delta }}{t}_{{\rm{O}}-{\rm{C}}}^{{\rm{lin}}}-{B}_{{\rm{quad}}}﹩, and the residuals after further subtracting the parity-dependent sinusoidal component, ﹩{\rm{\Delta }}{t}_{{\rm{O}}-{\rm{C}}}^{{\rm{lin}}}-{B}_{{\rm{quad}}}-{S}_{s}﹩. The middle panel shows the best-fit odd and even modulations together with their 90% credible bands, which reveals two antiphase branches. Right: same as the left, but for the shifted assignment N_{FinalEpochStart} = 422, which produces an apparent in-phase modulation between the odd and even branches.