HDG TRACK DEV IN A NON ADHERENCE TO ATC PROC CLRNC.

Narrative

WE WERE BEING VECTORED FOR THE VISUAL APCH INTO PDX. AFTER WE CALLED SEEING THE ARPT PASS MILL E OF PDX WE WERE CLRED FOR THE MILL VISUAL APCH TO RWY 28R; SIDESTEP TO RWY 28L. (AT THIS TIME WE WERE ABOUT 8-10 E/SE OF PORTLAND ON AN ASSIGNED HDG OF 010 DEGS). AS THE PNF I WAS BUSY TUNING AND IDENTING RADIOS AND RUNNING CHKLISTS. WHEN I LOOKED UP THE CAPT APPEARED TO BE 'CUTTING THE CORNER' ON THE VISUAL APCH. JUST AS I LOOKED UP PORTLAND APCH ASKED US IF WE WERE MAKING A STRAIGHT-IN VISUAL TO RWY 28L. I SAID THAT WE WERE ON THE MILL VISUAL TO RWY 28R; SIDESTEP TO RWY 28L AND THE CTLR THEN INFORMED US THAT HE SHOWED US ABOUT 3 MI OFF OF THE RECOMMENDED GND TRACK ON THE VISUAL. THE CAPT THEN PROCEEDED TO GET BACK ON COURSE FOR THE MILL VISUAL AND THE REST OF THE FLT OCCURRED UNEVENTFULLY. AFTER WE BLOCKED INTO THE GATE I DISCUSSED THE INCIDENT WITH THE CAPT. HE SAID THAT HE MISUNDERSTOOD THE CTLR AND THOUGHT THAT WE WERE CLRED FOR THE STRAIGHT-IN VISUAL TO RWY 28L. HE WAS VERY TIRED AND I SHOULD HAVE MONITORED HIM BETTER AND THIS INCIDENT WOULDN'T HAVE HAPPENED. NEXT TIME I'LL TRY TO EITHER FINISH CHKLISTS AND ETC. SOONER OR I'LL MORE CLOSELY MONITOR THE SIT WHILE I AM RUNNING CHKLISTS.