Guide

1. Right-click the table in the 'Navigation Pane' and choose 'Design View'.

2. Click the field you want to validate.

3. In the Field Properties pane, locate the 'Validation Rule' property. Click the ellipsis icon.

4. Enter your custom validation rule as an expression. Click 'OK'.

5. Enter a message in the 'Validation Text' property to display when the rule is violated.

6. Click 'Save' to save your changes and test the rule.