ACR WDB FRT DEVIATED FROM CLRNC ROUTE. WRONG LATITUDE SET IN INS.

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AN OFF TRACK ERROR OCCURRED AFTER PASSING OVERHEAD SYA ON ROUTE A590 ENRTE FROM TOKYO TO ANCHORAGE. I WAS THE CAPT AND HAD JUST LEFT MY SEAT TO GET SOME COFFEE AND USE THE HEAD. I WAS IN THE HEAD WHEN WE PASSED OVERHEAD SYA WITH THE NEXT POS AS 'PICUM' A NON-COMPULSORY RPTING POINT ON A 590. WE WERE IN CONTACT WITH ANCHORAGE CTR ON VHF. THE N COORD FOR PICUM WAS IN ERROR. PICUM WAS WAYPOINT ONE AND WAS IN THE INS AS 5-711.8 NORTH INSTEAD OF 5511.8 NORTH THE CORRECT COORD. THE F/O WHO WAS IN THE RIGHT HAND SEAT RPTED SYA TO ANC CTR ON VHF. HOWEVER HE DID NOT CHK THE COORDINATES FOR PICUM NOR DID HE SEE THAT THE ACFT WAS TRACKING TO THAT WAYPOINT EVEN THOUGH THE VOR RADIAL OF 55 DEG OUTBND FROM SYA WAS SET IN BOTH HSI'S. I DISCOVERED THE ERROR IMMEDIATELY ON RETURNING TO MY SEAT WHICH WAS ABOUT 10 MINUTES LATER. I CORRECTED IMMEDIATELY BACK TO COURSE. HOWEVER WE WERE ALREADY ABOUT 20 MI NORTH OF COURSE AT THE TIME. THE F/O HAD FAILED TO SEE THE ERROR AND ANC CTR DID NOT WARN US AT ANY TIME WHEN WE WERE GOING OFF COURSE EVEN THOUGH THEY ALWAYS HAVE ACFT ON RADAR IN THE SYA AREA AS THEY DID THIS TIME. WE DID NOT TALK TO ANC CTR AFTER SYA UNTIL THE NEXT REFERENCE POINT ST PAUL ISLAND. I BELIEVE THAT THIS ERROR OCCURRED BECAUSE BOTH PLTS WERE NOT IN THE SEAT DURING A COURSE CHANGE TO CHK ON THE CORRECT CHANGES IN THE INS AND A/P. THIS I WILL SEE TO IN THE FUTURE.