(a) Transitions of trans-MF identified (A-symmetry substate) toward L1157-B1 (listed in Table 1) sorted by increasing frequency. The result of the best LTE fit of trans-MF is plotted with a red line (observed spectra shown as black lines and gray-shaded histograms). (b) Velocity stack of the observations (in gray) with the corresponding stack of the LTE simulation using the best-fit parameters to the individual lines (in red). The RMS of the stacked spectrum is 0.36 mK, implying an integrated signal-to-noise ratio (S/N) of 11.6.