2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/87207As a note for paper [physics/0505035], this is to make it more clear how we can depend upon Einstein's theory of gravitation and two assumptions of the cosmological principle and perfect fluid, in the so-called Z-approximation, to construct a solvable model of cosmology in the Earth-related coordinate system. Hence, the cosmic acceleration becomes understandable.3 pages with no figureGeneral Physicstext