Difference of at fixed (V − I)^TRGB colour when varying – one at a time – the labelled physics inputs and computational time steps (see text for details). Filled circles in the various panels display the cases with Δt_min = 3 kyr time steps, Δα_MLT = +0.2, and NACRE reaction rates for all nuclear reactions (including the reaction). Open circles display the cases of weak screening, Δt_min = 0.3 kyr, Δα_MLT = −0.2, and NACRE rates plus the LUNA rate for the ¹⁴N+p reaction.