This explains the “knobs” you’re asking about.
I found this helpful too; you’ll want to scroll down to “Frequencies” section.
Maybe this posting helps?
I’m in the US so haven’t had to understand it deeper 
This explains the “knobs” you’re asking about.
I found this helpful too; you’ll want to scroll down to “Frequencies” section.
Maybe this posting helps?
I’m in the US so haven’t had to understand it deeper