Evolution in time of the dispersion in the η′ coordinate for a simulated YLA with initial conditions IC-1 and following orbit-1, from left to right, with ages of 20, 50 and 80 Myr (marked with a vertical black dashed line). The different colour lines are the intrinsic dispersion (σ_int, cyan dot-dashed line), the propagated observed dispersion (σ_obs, dark-blue solid line), the dispersion due to observational errors (σ_err, red dotted line) and the estimated intrinsic dispersion (σ_est, green thick solid line). The grey-shaded region represents the uncertainty in the dynamical age determined.