In the atmosphere, the factor (3Γ₁ − 4) < 0 can give rise to dynamical instability (cf. Ledoux 1958, 1965) when this factor is negative. Using data from Meynet models (Meynet et al. 1994, and priv. comm. 1997) and code from Nieuwenhuijzen & De Jager (1995), the value of Γ₁ during the evolution of m040e020 is calculated for τ_Ross = 2/3 (at the“radius” of the star) and plotted against effective temperature, using the same direction as shown in the HR-diagram. The dynamical instability limit is indicated: Γ₁ values below this limit can give rise to dynamical instability if the layer where this value is negative is “large” enough (Ledoux 1958, 1965).