2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/1181I describe a new technique that we have been using in the past few years to get precise measurements of the frequency separation of the kHz QPOs in some Low-mass X-ray binaries. I show how this technique (that we call "shift-and-add") works, and I present some of the results we obtained using it.To appear in the Proceedings of the NATO ASI School "The Neutron Star - Black Hole Connection" (Kluwer Academic Publishers), C. Kouveliotou, J. van Paradijs, J. Ventura (eds.). (6 pages; 4 figures)Astrophysicstext