Update negative number of days for Current Invoice and positive for past due

Hi,

1. I have a bill, for which I want to create negative number of days for Current Invoice and positive for past dues.

Kindly suggest how this can be achieved? I am functional consultant and I need to update this in Functional Specification so that the ABAPER can do the work.

2. In the Information Box for updating the details like

Customer Number

Statement Date

Closing Statement Date

Collector Name (Accounting Clerk name-KNB1-INTAD)---To be Added

Collector Email ID (Accounting Clerk Email- KNB1-INTAD)----To be Added

What should be the logic to add this in Functional Specification?

Collector Name (Accounting Clerk name-KNB1-INTAD)---To be Added

Collector Email ID (Accounting Clerk Email- KNB1-INTAD)----To be Added