There's no need for the setFocus command. Also, if you want to validate a value then you should use the Validate event, not the Format event.
In the Validate event you can also reject an incorrect value by setting event.rc as false.
Many thanks Gilad, just one quick one...
Any thoughts on the 'if' with no 'else'? Or is it just a subjective preference?
It's not a problem.