  The parameters of the Bose-Einstein correlation function may obey an {\it $M_t$-scaling}, as observed in $S + Pb$ and $Pb + Pb$ reactions at CERN SPS. This $M_t$-scaling implies that the Bose-Einstein correlation functions view only a small part of the big and expanding system. The full sizes of the expanding system at the last interaction are shown to be measurable with the help the invariant momentum distribution of the emitted particles. A vanishing duration parameter can also be generated in the considered model-class with a specific $M_t$ dependence. 
Bose-Einstein Correlations for Three-Dimensionally Expanding,   Cylindrically Symmetric, Finite Systems