Want a neat trick you can use to make your worksheets more helpful to users? How about adding a pop-up window that displays documentation whenever the cell is selected? To add such a feature, follow these steps:

1. Select the cell for which you want the pop-up to appear.
2. Choose Validation from the Data menu.
3. Make sure the Input Message tab is displayed. (See Figure 1.)



Figure 1. The Input Message tab of the Data Validation dialog box.

4. Make sure the Show Input Message When Cell is Selected check box is selected.
5. In the Title box, enter a title for the pop-up window. (This title appears in bold at the top of the pop-up window.)
6. In the Input Message box, enter the text of the documentation you want to appear in the pop-up window.
7. Click OK.

There are, obviously, other ways you can use the Data Validation feature of Excel to check and limit the data that is entered in a cell. However, if you follow the steps above, all data is still accepted, and Excel displays a helpful message whenever the cell is selected.