Well, the AD2 is really a (software defined digital) scope with FFT ... so the front end is a scope front end, the probes are high impedance voltage input. Therefore the display is relative to voltage, not power. I can't choose dBm ... BUT ... the measurement between the fundamental and the harmonics and spurs are relative, they are dB down from fundamental. Changing the reference changes the scale on the left, but not the difference between the peaks. (Unless I am doing the decibel math wrong, which is possible).
On mine -- on 12m -- with mike gain and RV1 turned down -- I'm calling it FCC compliant with all peaks 43dB down from the fundamental on 12m, either SSB or CW.