These two concentric knobs are used to spell out ID names.
Additionally, if the smaller (inner)
knob (labeled "PUSH CRSR") has been pushed, the knobs are turned to move the cursor
on the screen.
In the moving map screen, if MENU is clicked and "Measure
Distance" is selected, the two
knobs are used to move the cursor through the X and Y axes. It can also be used to query
airspace limits (extremely useful in Class B areas).
If the cursor has not been activated and no other option
lists are shown, turn the large knob
to change Groups ("chapters") and small knob to changes Pages within the groups. The
current Group and Page is shown at the bottom right of the screen in the Page Group Window.