2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/135473A technique for background prediction using data, but maintaining a closed signal box is described. The result is extended to two background sources. Conditions on the applicability under correlated cuts are described. This technique is applied to both a toy model and an analysis of data from a rare neutral kaon decay experiment.8 pages, 8 figures, submitted to PRDData Analysis, Statistics and Probabilitytext