2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/36385We define a Frame of reference as a two ingredients concept: A meta-rigid motion, which is a generalization of a Born motion, and a chorodesic synchronization, which is an adapted foliation. At the end of the line we uncover a low-level 3-dimensional geometry with constant curvature and a corresponding coordinated proper-time scale. We discuss all these aspects both from the geometrical point of view as from the point of view of some of the physical applications derived from them.Latex, 32 pages Journ-ref: To be published in "Gravitation and Relativity in General", Ed. A. Molina, J. Martin, E. Ruiz and F. Atrio. World Scientific (1999)General Relativity and Quantum Cosmologytext