Use Cell Validation to create rules that will disallow edits (or show warnings) if the data changes in ways that you wish to prevent or be notified of. This is designed to complement, but not replace, server validation.
You are able to prevent the edit or to show a warning and when creating rules, you can select from a huge list of operators regarding the change.
This example has 4 Validation Rules: (1) All Edits are prevented in the 'Cust Ref' column; (2) warnings are displayed for all edits in 'Employee' column; (3) The 'Invoiced' Column cannot accept values over 3000; and (4) a warning is shown if the 'Order Cost' column more than doubles in value. Note: these cell validation rules apply also when you perfrom a Smart Edit or Bulk Update.