Avidyne IFD540 Pilot's Manual page 33

Virtual Numeric Keyboard
Each keyboard has a scratchpad in the lower right corner. The
scratchpad is a free text field for data entry with some data entry
validity logic applied to the data that is trying to be entered. For
example, when trying to type in an invalid frequency, the com
tuning application will immediately sense that entry to be invalid
and present an alert box stating the entry is invalid.
Invalid Keyboard Entry Alert
System Overview 1-27