Full table scan: what order?

I've written a script (or at least tried) that shows me how far a full table scan has progressed for a session. I can determine the block the session is currently reading by retrieving p1 (file_id) en p2 (blocknumber) from v$session_wait in case of event 'db file scattered read'. But in which order does Oracle read the blocks?
- file_id,extent_id?

• extent_id? Is there a difference between Oracle 7 and Oracle 8? I've tried both assumptions but the result my script is giving is never a steady increasing value.