EC sales report - EU check Box in Billing Document

Hi Experts,

Thanks for all your responses. I have a question on EU traingular

Check box In billing Document.

As per Client requirement, that while creating the billing document,

the check box should gets checked automatically in billing docuemnt.

1) Can somebody help me understand how can we make this automatically.

2) What is the business use of having a seperate list of EC sales for

checked box and EC sales without checked box.

Arpit