Audit Trail Code Confusion

Let’s take a sales transaction. When looking at the Audit Trail Code Setup I see Source Document code of SJ for Sales Journal.  OK, no problem understanding that.  Then I see a Prefix Column & Next Number which is used as an audit trail number on the Sales Posting Journal.  But it is NOT the audit trail code in the GL.  Now it becomes the Batch Id.  Huh?  

I’d really like someone to take me thru a scenario where they have to find a sales transaction or any subledger transaction via the audit trail code from the GL back to the subledger.  Step by step.  It seems very confusing trying to track down a transaction from the GL to the subledger since the GL has it’s own Audit Trail code.   Thanks.