Phase shifts between the five temperature maps obtained from the SONG data for set01–set05. The constant movement of the spots has been removed from the measurements, by removing the shift at the lowest latitude (ψ_* = 60.25°) that always has spots. The plot gives the average phase shifts in degrees per day plotted against sin ² (ψ) − sin²(ψ_*). The error bars indicate the standard deviation. The weighted fit of the function f(ψ) = β(sin²(ψ) − sin²(ψ_*)) to the measurements is shown as a straight line.