Is there a way to create some sort of masking sheet over a current data sheet
that, when I re-input data, can tell me if there is a discrepancy between the
two values. For example, on Data Sheet 1, I have the value 98765, and when
re-entering the data, I mistype 11234, Excel can notify me of that problem?

This is for the purposes of verifying numberic data that has been entered
into a speadsheet. Thanks!