Data Entries with Data Validation
This tutorial acquaints you with a very versatile and, in the long run, great timesaving feature that Excel calls data validation. You use this nifty feature to prevent the users of your spreadsheets from ever getting a chance to enter the wrong type of data entry or a type that's not on your list (when dealing with labels) or within a tolerable range (when dealing with numbers) in critical cells of its worksheets.
Not only can you restrict the types of data entries that you or any other spreadsheet user can make, you can also add input messages to your validated cells that indicate what types of entries are permissible there. As if this weren't enough, you can also tag the validated cells with error alerts that flash an alert symbol along with a custom message indicating the data entry rules for the current cell!