Top: positions of the absorption peak for an absorption line search centered on 1423.4 MHz. Only eight of these have peak S/N>6, and none have S/N>7. Bottom: Same as the top panel but for the absorption lines searched in the negative (−1.0×flux) spectra centered on 1423.4 MHz. Less than 10% of the absorption features have peak S/N>6 (see text for details). The blueshifted frequency range considered here is beyond all H I 21-cm emission ever observed (Putman et al. 2012).