HP 8591C User Manual page 183

Channel Measurements Menu Map and Softkey Descriptions
Channel Measurements Softkey Function Descriptions
5. Press the AVERAGE ON OFF softkey to perform a trace averaging function
to smooth the trace.
6. In the carrier-to-noise measurement, press INTGRTN RNG SET to position
the two markers within the desired measurement range.
Rather than using a single measurement point, the INTGRTN RNG SET
made. This accounts for the non-flatness of the noise floor.
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