You may have imported or entered account codes into a Microsoft Excel spreadsheet and want to identify invalid account codes. Let's say the account codes are supposed to have five characters but because of data entry errors some accounts codes do not meet the required criteria; they either exceed or are less than five characters.
By using the Data Validation option to circle invalid data the invalid account codes will be circled and therefore easily identifiable. It must be noted that data validation will have to be applied before circling invalid data. Circling Invalid Data can only be applied with data that has already been captured, unlike with Data Validation which can also be applied prior to data being captured.
Full article: Circling invalid data
