Excel's data validation tools help make sure funky data doesn't end up in your worksheets. But they don't protect your worksheets against things like accidentally deleted formulas, mistakenly scrambled formatting, and "unintentionally" modified Maximum Deficit Spending values. To defend against these dangers, you need to use Excel's worksheet protection features.
Figure 24-11. The list validation settings in this dialog box tell Excel to generate a list of product choices drawn from the range of cells indicated in the Source box. See Figure 24-10 for what this looks like on the spreadsheet.
To understand how worksheet protection works, you need to know that each cell can have one of two special settings:
Locked. When a cell is locked, you can't edit it.
Hidden. When a cell is hidden, its contents don't appear in the formula bar. The cell still appears in the worksheet, but if the cell uses a formula, you can't see the formula.
You can use these settings individually or together. When a cell is both locked and hidden, you can't edit it, or view it in the formula bar. On the other hand, if a cell is hidden but not locked, people can edit the cell but can never tell whether the cell uses a formula, because Excel keeps that information secret.
The most important thing you need to understand about locked and hidden cells is that these settings come into effect only when ...