Mean dependence of cyclotron line energy on pulse phase for the Main-On of 35 d cycle 323, as observed by RXTE/PCA in 2002 November. The solid red line represents a best fit function (a combination of two cosine components). Normalized pulse profiles of the 30–45 keV range are shown for five different 35 d phases: 0.048 (black), 0.116 (red), 0.166 (green), 0.21 (blue) and 0.24 (purple). The main pulse is progressively moving to the right. The right hand scale is normalized flux (0–100) for the pulse profiles.