How does Gqrx calculate the signal strength reported by the remote server?

[KTH21]

I have been using the Gqrx remote server and the Mac Terminal tool to look at signal strength values.  The signal strength values are reported from the remote server in units of dbm.  

I would like to know how the Gqrx system calculates the values.  Does it take an average of the signal strength across the passband of the filter in use?  In that scenario, the value of an AM signal might be the average of the frequency band from the carrier-2000 Hz, to carrier+2000 Hz.  Also in that scenario a USB or LSB signal might be calculated as the average of the spectrum from carrier to just +2000 for USB, and the opposite for LSB.but would not include the area where the carrier is located in an AM signal.  And then, for CW it might be just the very narrow CW, CWL, or CWU range.   On another hand, maybe the signal strength is just some narrow point where the carrier is located.  If so, that wouldn’t work for SSB signals.  

So, the question is, how does Gqrx calculate the dbm value that is reported via the remote server?