Avidyne IFD540 Pilot's Manual page 113

When you have finished loading frequencies into the preset slots,
exit the edit mode by either touching the "Edit" box again or using
the bottom right IFD knob to highlight it then push the knob in.
To nominate a frequency from the com preset list into the #1
Standby slot, make sure it is highlighted by either touching it or
using the bottom right IFD knob. Then either touch it a second
time or push in the IFD knob.
For aircraft with the cockpit control installed (e.g. dedicated com
preset button on the yoke), any time it is activated, it will briefly
display a small dialog box next to the #1 Standby slot indicating
which preset slot is used.
#1 Standby Slot
If the com preset page happened to be displayed at the time the
cockpit control was activated, a small arrow will indicate which
preset is used.
Com Preset Arrow
Each subsequent actuation of the cockpit control will step to the
next non-blank entry in the com preset list.
AUX Pages 4-5