Just checked it myself now - I did not notice it before!
This setting is actually quite interesting, as it corresponds to the Video Bandwidth setting of spectrum analysers.
A short explanation here:
What is Video Bandwidth? - everything RF
This makes the spectrum analyser mode of the HD Ranger series quite powerful, as it includes RBW and VBW like any regular spectrum analyser.
Among my collection of field meter, I have to say that the Promax HD Ranger series is quite impressive, both function- and performance-wise.
It is the only device in my collection that will for instance show the HbbTV URL (Hybrid broadcast broadband TV -
HbbTV) of any channel supporting it. I think that newer Promax field meter equipped with Ethernet allow to actually show HbbTV on the device itself.