2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/168477In this paper we derive the Schroedinger equation by assuming it describes the time evolution of a deterministic and reversible process that leaves at each moment in time a different observable well defined; that is, it allows an accurate prediction for it. We also derive an expression for the well defined observable and apply this expression to the cases of spin precession and a free particle.5 pages, no figures, submitted to AJPQuantum Physicstext