fx-9860GII
UNDO
On a Casio calculator you can undo the last operation
INS UNDO ALPHA DEL
To redo an operation you just undid you must press it again.
Example 1
To undo a fraction
INS UNDO 1 2 3 4 5 ab/c ALPHA DEL 12345
Example 2
To undo the deletion of a digit
INS UNDO 12345l
DEL 1234l
ALPHA DEL 12345l