2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/102987We compute the linear responses of the Hubble diagram to small scalar perturbations in the Robertson-Walker metric and to small peculiar velocities of emitter and receiver. We discuss the monotonicity constraint of the Hubble diagram in the light of these responses.9 pages LaTeX, no figureAstrophysicstext