Create a task custom field ( please note, needs to be a numeric field like number or cost). In my example I simply called it Test.
You will see that the project custom field will take the task custom field (which normally is not the case).
Save the custom field and now you will be able to use the task custom field to either enter data ( or calculate based on a formula ) and at the same time the project custom field will show the value of the sum of the task custom fields.
---- Task vaues are entered and summed ----
--- Project custom field displayes the task custom field value ----
This function will allow you to add summarises task custom fields into the Project Center for example ( e.g. total work for development tasks ). A great way to give more project details to key stake holders. Not to mention the reporting cababillities. Thanks Laith great way of dealing with this.