Spectrum analyser - scale of y-axis

[timxhub]

On the spectrum analyser screen, I know that the x-axis goes from 400 to 406 MHz and that the y-axis starts at -125 (as set in the noisefloor parameter).

What I cannot find in the documentation is the scale of the y-axis. Please could someone tell me what it is, or how it is calculated, or point me to the answer in the documentation?

Also, on some of my devices the no-signal spectrum level is quite high up the graph. Does anyone have any suggestions for setting noisefloor or is it just a case of trying different values, for example -110?

I have T-Beam with AXP2101 (plus some other boards). They have the 0.9" OLED display.
Version: dev20250218.

Thanks.