Hi @AudioGarden, the scales are almost always fixed in dB. The plots you see above with white background are automated measurements and if you are measuring THD(N) then the left axis will shown dB and the right axis will show %.
In the analyzer (dark background) you can switch between dBFS, dBV, dBU, and dBR. The dBFS is useful if you want to understand your measurements relative to full scale on the converter. The dBR is, of course, relative measurements. You can also switch between freq domain and time domain. But the time domain shows things relative to dBFS. In other words, the time domain is primarily for sanity checking what you are seeing in the frequency domain.
In the measurements shown on the top of the display, those are most all in dB (as specified by user). The one exception is the RMS measurement. You can opt to display that as a linear measurement (eg 0 dBV displayed normally, but 1 Vrms displayed if you select linear). And the peaks can be displayed in watts if you specify a load impedance. THD(N) are always shown as dB and % together (no way to turn one off).
The generator voltage level is specified in dB always.Let me know if you have other questions or would like to see other measurements.