Learn how to create a drop-down list using Data Validation in Excel. Data Validation limits the type of data that can be entered into a cell.

Now, create a new number list in the next adjacent column (see the above screenshot). You have to use this number list to reverse the list in Excel.

This creates a long list of unique identifiers. You may use any number to increment the value, such as altering the formula to "=A1+567," to create a less obvious pattern.

Figure B How to return a sequence of dates in Excel Excel’s fill handle can generate a quick list of dates for you, but the list is static; you must create a new list if your needs change.