Stellar evolutionary tracks in the HR diagram in the main-sequence stage. The dotted lines correspond to the standard stellar models in which the convection heat flux is calculated using MLT and overshoot mixing is absent. The dot-dashed lines correspond to the classical overshoot stellar models in which the convection heat flux is calculated using MLT and the overshoot leads to complete mixing in 0.4 H _P outside the boundary of the convective core. The solid and dashed lines correspond to the stellar model with TCM and diffusive overshoot mixing. The value of C _X1 for solid and dashed lines is 10 ⁻³ and 10 ⁻², respectively.