This video shows you how to idiot-proof a data set in Excel pretty much. It demonstrates how to enable data validation in a cell, so that when you type something in it must be in a predetermined list or will not work. Start by typing in your data table in a second tab. His example is a date, then information about certain employees based on that day. To enter the data validation menu, click the cell you want to use and then hit ALT+D+L to bring it up. Go to settings, then under the Allow menu. Un-check the in-cell drop down button, and then click on List under the Allow menu. Type in the source for your data table, and hit enter. Now when a date is typed in, it must be in the list or it will not work.