Left: observed relative amplitude behaviour as a function of wavelength for P₂ = 145.8 s, depicted by the black points with error bars. Each point represents a 130 Å wide bin of the original monochromatic quantity, which was averaged in order to improve the S/N. The error bars indicate the rms deviation about the average value within the wavelength bin. The predicted monochromatic amplitudes for different degree indices are also shown and labelled. All quantities have been normalised. Right: similar to the left panel, but referring to the relative phase.