Distribution of differences among the detected frequencies (every frequency was subtracted from all the others and the plot is restricted to the positive values). For easier comparison, each histogram is normalized to the local maximum around 7 d^-1. The black line refers to the whole set of 403 frequencies, the gray line to those with amplitude larger than 10^-4. The histograms show that there is a preferred spacing around 2.3 d^-1, which is clearly visible in both distributions. According to Breger et al. (2009), the spacing corresponds to spacing between radial modes. The multiples of the spacing are also indicated by dotted lines.