Profile differences δ_tΓ₁/Γ₁ again obtained for a fixed value of δY_s = 0.25, but from a pure-hydrogen reference model Y_s = 0. The 500 profile differences in this plot were obtained by randomly drawing the remaining two reference quantities (ψ_CZ, ε) in the 2D box [ − 9, −3]×[0.015, 0.02] (the ε interval has been reduced compared to Fig. 8 for clarity). Two opposite corners of this box are highlighted in red and blue.