Convergence of the numerical simulations to the model for a p₁-ridge with an observation time T = 8 h. The errors Err_i(n) defined by Eqs. (25, 26) are represented for Var [ τ_diff ] and for travel times between two points separated by a distance Δ = 10 Mm. The dashed lines have a slope of 1/2 and show that the error decays as .