Format a cell to always be negative

[lisach]

It seems Excel can do anything we want it to. But, can you format a cell so that when a number is entered into it by someone that it will always be negative? I tried adding a comment to the cell to warn users to enter it as negative but if the user is using the tab or enter button the mouse focus doesn't land on the cell and the comment doesn't pop up. I need to make sure that number is always negative.

Thanks in advance for all your help and suggestions.

[Palmetto]

Formatting only changes the way a number is displayed, not the actual underlying value.
Use Data Validation.
Under the Allow drop down choose either Decimal or Whole Number.
Under the Data drop down choose "less than" and enter zero as the Maximum.

Go to the Error Alert tab in te dialog and set the Alert Style to stop and create a custom error message for users.

[lisach]

You are incredible! Thank-you! Thank-you Thank-you! Works perfectly!