A spectrum analyzing device and method include sweeping a first frequency range at least once at a first resolution and performing a Fast Fourier Transform (FFT) on data from the sweeping of the first frequency range to produce first peak hold trace data. A second frequency range is swept at least once at a second resolution and an FFT applied to produce second peak hold trace data based on the sweeping of the second frequency range. The resolution for the sweeps is selected based on a bandwidth of the frequency range to be swept. A composite graphical display is produced based upon the first and second peak hold trace data. By caching the peak hold trace data, the spectrum analyzer preserves detected signal information when zooming from a coarser to a finer frequency resolution while minimizing the processing requirements of the spectrum analysis.