Calligra Sheets can automatically check the validity of entered data against a number of criteria, and pop up a message box if the data is invalid.

To enable this feature, select the cell(s) to be monitored and choose Data → Validity.... This will bring up Calligra Sheets's Validity dialog box which has three tabbed pages.

In the Criteria page select what type of data is to be considered valid from the Allow: combo box list then define the valid range of values by choosing one of the options in the Data: combo box and entering suitable value(s) into one or both of the edit box(es).

When you have done this change to the Error Alert tab. Here you can choose the type of message box (Stop, Warning or Information) that will appear when an invalid value is entered, and define the message box title and message text.

Note that this feature only checks data that you enter into the cell, for a way of checking the results from formulae cells see the Conditional Cell Attributes section of this Handbook.