2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/149620We enhance elementary quantum mechanics with three simple postulates that enable us to define time observable. We discuss shortly justification of the new postulates and illustrate the concept with the detailed analysis of a delta function counter.25 pages, LaTeX, 6 postscript figuresQuantum PhysicsCondensed MatterFunctional AnalysisGeneral Relativity and Quantum CosmologyHigh Energy Physics - Theorytext