If you've used data validation in Excel before, you probably selected the relevant cells, clicked "Data Validation" in the Data tab on the ribbon, and created the rule in the Data Validation dialog ...

Locating missing sequential numbers can be an arduous task when working with long lists of data. For example, you might want to locate business check numbers that haven't been logged into a balance ...

Excel's VALUE function has only one argument: where a is the value stored as text that you want to convert into a number.