Sketch of broadband galaxy shape (open contours) and the spectrogram for an infinitely thin emission line (shaded contours) distorted by intrinsic velocity curve (red dashed line); x (resp. y) is direction of dispersion (resp. cross-dispersion), PA is the intrinsic relative position angle defined as the angle between the broadband galaxy major axis and the cross-dispersion direction, and PA_eff the apparent position angle on the spectrogram.