Experimental estimates of τ₁ are compared with the model τ_MLT (Noyes et al. 1984). Top panel: relation of individual estimates of log (τ₁) (crosses), their average values in the 300 K-intervals of T_eff (squares with error bars), and log (τ_MLT) (dashed curve) with stellar effective temperature T_eff. The solid line of log (τ_MLT) + 0.82 well approximates the experimental data. Bottom panel: comparison between log (τ₁) and log (τ_MLT) shows a near-linear relation. The slope of the linear regression line (solid) is 1.13 ± 0.06.