NeoCal for Palm OS User Guide
The last ten operations can be reverted by selecting the Undo menu option from the Edit menu. An undo operation can be undone by selecting the Redo menu option. The entire state of the calculator, including stack and register values, are restored to the state before the previous operation was performed. Continue selecting the Undo operation to continue reverting the calculator to previous states.
When another operation is performed after an undo operation, the redo information is lost. Also, the undo information is lost when switching to another application.
The button should be used to correct mistakes while entering numbers, as the undo operation will undo the entering number operation.
Settings in the Preferences dialog are not affected by the Undo/Redo operations.