B&K Precision 2542B-GEN - Manual - Manual (Page 51)

Basic Operation
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Example:
Select CH1 as the Source for FFT, select Rectangular
Window, set Scale to dBV RMS, and then the FFT waveform
will look like below. You can also measure the amplitude and
frequency of the corresponding point with the manual cursors
(See “CURSOR Menu”).
FFT Spectrum Analysis