Petersen diagrams of the two types of common additional modes in RRc stars. Upper panel: f_0.68-type modes. Given the multitude of frequency peaks in V14 and V16, we include ratios between two possible sets of peaks. Lower panel: f_0.61- or f_X-type modes. Here, we plot the regular f_X modes with X crosses, whereas + signs mark the positions of the f_X/2 peaks when doubled. For V04, we also show the peak and FWHM of the Lorentzian fit to the peaks with the pink point and line. Note: in V03, the respective peaks overlap indicating that we observe the half of the f_X peak, but in V04, the f_X/2 signal lies outside of a pattern of f_X frequencies. Here, we again show two possible ratios for V14. Underlying points are from Molnár et al. (2022) and references therein.