8.3 GHz GBI observations (red squares) and model (black stars) data. All phases, Φ, refer to (t − t₀), with t₀ = JD 2 443 366.775 (Gregory 2002). a) vs. Φ (P₁) (orbit P₁ = 1/ν₁ = 26.49 days); b) vs. Φ (P₂) (precession P₂ = 1/ν₂ = 26.92 days); c) 8.3 GHz GBI observations before (red points) and after (green points) 50 841 MJD vs. Φ (P_average) (P_average = 2/(ν₁ + ν₂) = 26.70 days). The points cluster separately with a shift of 0.5 in phase. The model reveals the same double clusterings: Black points refer to model data before 50 841 MJD and blue points to model data after 50 841 MJD.