These two concentric knobs are used to dial in the
for the COM and
NAV (VLOC) radios. The larger (outer) knob controls the digits to the left of the decimal
point. The smaller (inner) knob controls the digits to the right of the decimal point.
Since the knobs control two radios, a method is needed to
specify which radio they are
referring to. Press the smaller (inner) knob to toggle between the COM and VLOC
radios. The blue highlighted cursor bar indicates which is the active radio.