Petersen diagram for 0.61 and 0.68 stars. The green points correspond to Cepheids from the SMC, the blue points correspond to Cepheids from the LMC, and the red points correspond to Cepheids from the Galactic disk (Rathour et al. 2021). Our stars are plotted with black asterisks using values based on the FWHM. The interpretation of individual sequences, i.e. the degree of the non-radial mode, according to the theory by Dziembowski (2016) is marked in the figure.