Excel Data Validation

The Excel Data Validation feature allows to set up rules that determine what can be entered into a cell. A custom message can also be displayed when the entered value doesn't satisfy the set conditions.

Evaluation of Formula
The example below limits the data entry in cell E4 to whole numbers between 1 and 100. If the user makes an invalid entry, a custom message, such as the one shown below will pop-up.

Setting-up the Data Validation
Select the cell or cells that you want to limit the data entry then access the data validation feature via Data > Data Validation. A small window will come out to set the rules and customized message can be defined when the entered data is invalid.