Excel - trapping invalid data

There's a term that I love called GIGO - garbage in garbage out. When you're designing an Excle worksheet to solve a business problem you need to make sure that your data is correct or your worksheets won't give valid results.

Luckily, Excel's Data Validation tool helps you prevent incorrect data being added into your worksheet.

To set up a validation rule and to configure what will happen if incorrect data is entered, start by selecting the cells to which the rule should apply. Choose Data, Validation, Settings tab. Now, for example, to limit the data being entered to a whole number less than 200, select whole number from the Allow drop down list. When the Data area appears, choose Less Than and then in the Maximum area type 200.

To configure a user message to tell the user what is required, click the Input Message tab and type a title and a piece of explanatory text telling the user the limits to the type of Data you're expecting them to enter. This appears as a tooltip entry when any of the cells configured with the data validation rule is selected.

You can also specify what should happen if a user enters an incorrect value. To do this, click the Error Alert tab and select the type of indicator from the Style list. If the user enters incorrect data and if you have chosen the Stop style they will have two choices - Retry and Cancel and the invalid data cannot be entered into the cell. The Warning and Information styles both warn about the incorrect data but still allow it to be entered.

Once you've chosen the style, enter the Title and the Error Message which the user will see if the data in not correct. Click Ok and you can now test the rule.