Agilent Technologies ESA Series User's/Programmer's Reference page 56

Front-Panel Key Reference
Auto Couple
The detector displays the minimum of the signal within
Negative Peak
the bucket.
Neither average nor sample detectors measure amplitudes of CW
signals as accurately as peak, because they may not find a spectral
component's true peak, but they do measure noise without the biases of
peak detection.
The detector in use is indicated on the left side of the display. A # will
appear next to it if the detector has been manually selected.
Key Access:
Auto Couple
The system selects peak detection as the default, but if
Auto
a condition arises where a different type of detection
scheme provides greater accuracy, the system will use
the alternate scheme. For example, when using the
Marker Noise function, Auto mode selects Average
detection for Res BWs > 300 Hz and Sample for Res
BWs ≤ 300 Hz as shown in
Key Access:
56
Figure
Auto Couple, Detector Auto Man
2-1.
Chapter 2