The options are 12, 24, 42, 60, 78, & 90.
Choosing one of these numbers sets the scale of the meter to a certain range of dB. For example, choosing -90 dB sets the range of measurement of that meter to 90 dB.
You can also change the scale of a meter by right-clicking the meter to display a pop-up menu and choosing a new dB range.
The "non-segmented" "B" meter is where you will notice this the most as it displays the number scale.

However, the Console View Mains will always revert to the 42 dB scale no mater which one I select.
>Why don't you install X3D, recommended :) Can you verify that X3d does not have this issue?
Thanks,
Steve