The document discusses using zero span mode on a spectrum analyzer to view transient signals over time at a fixed frequency. In zero span mode, the display changes from amplitude vs frequency to amplitude vs time. The resolution bandwidth setting determines what bandwidth of the signal around the center frequency will be visible. Very narrow bandwidth signals like a CW carrier only require a 10 kHz resolution bandwidth to view, while wider signals like NTSC video need at least 300 kHz to see details. Zero span allows measuring the levels of intermittent signals like cable modem bursts and observing noise floors when the signal is not transmitting.