2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/106753All energy measurements of a quantum system are prone to inaccuracies. In particular, if such measurements are carried over a finite period of time the accuracy of the result is affected by the length of that period. Here I show an upper bound on such inaccuracies and point out that the bound can be arbitrarily small if many copies of the system are available.5 pages, no figures. Contains the derivation of results presented in quant-ph/0412073 and quant-ph/0304206Quantum Physicstext