H Heuer Instruments UMDT51A User Manual page 53

Making Measurements
Setting the centre frequency and adjusting the frequency span, enables a
portion of the frequency spectrum to be expanded (or zoomed in). The following
example, where there are two tones close to 1,000 kHz illustrates this feature.
Examining the spectrum from baseband with a span of 1,200 kHz, it is clear
there are two peaks close to 1,000 kHz, but they cannot be resolved easily.
Setting the Centre frequency to 1,000 kHz and the frequency span to 75 kHz,
zooms in on the peaks and reveals peaks at 991 kHz and 1,009 kHz.
LT51 User Manual 41