When you're entering large amounts of data, it's easy to type an incorrect value by mistake. To help avoid errors in your data, you can use Excel's data validation feature to check entries automatically and flag those that may be wrong. For example, if every entry in a range of cells should be between 250 and 1000 (inclusive), you can validate the data to flag any entry that is not in that range.
CAUTION: Data validation works only when the user types in a value. If the user pastes in a value, Excel doesn't validate it.
To apply validation to cells, follow these steps:
Validate(clicking the main part of the Validate button) from ...