Business rule not working

Hello,

I have a very simple business rule on the opportunity entity with the intended result being to update the value of the Actual Revenue field with the same value as has been entered in the Esitmated Value field, the condition to check is that the opportunity status equals WON.

This the business rule:

If Status Equals Won

Set Actual Revenue to Estimated Value

Background information in case it matters, I have a workflow which updates the status of the opportunity to won based on certain fields being completed on a different entity, the workflow works as expected.

Any ideas why the business rule will not work or a better way to achieve what I require?

Thank you

JazB