Brunt-Väisälä frequencies as a function of internal mass for five different star models at the beginning of the CHeB stage (top panel). The orange, green, red, and violet lines represent models calculated using the CLES, MESA, and BaSTI-IAC evolutionary codes (see Section 3), while the blue line corresponds to the fiducial barotropic model discussed in Section 3. All models are for a 1 M_⊙ CHeB star with solar metallicity. The red line represents a MESA model computed with the boundary mixing prescriptions outlined in Appendix F. These models reveal common features in their Brunt-Väisälä frequencies, including a convective core, radiative core, hydrogen-burning shell, radiative envelope, and convective envelope (the latter not shown for clarity). The bottom panel shows the helium mass fraction as a function of internal mass for four of the five models.