WT AND BAL MISTAKE BEFORE TKOF.

Narrative

WE WERE RECEIVING A LINE CHK FROM THE FAA. I HAD PREPARED THE WT AND BAL AND THEN NOTICED I HAD NOT ENTERED THE 170 LBS FOR THE JUMPSEAT OBSERVER. THE COMPANY HAD MOVED THE PERFORMANCE AND BUGS CHK FROM THE TAXI CHKLIST TO THE AFTER-START CHKS 2 WKS PRIOR. FEELING RUSHED; I CROSSED OUT THE ERRONEOUS WTS TO ADD THE 170 LBS. IN DOING SO; CALCULATION ERRORS WERE MADE; WHICH WERE NOTICED BY THE FAA OBSERVER ON THE TAXI OUT TO THE RWY. HE EXAMINED THE WT AND BAL SHEET FOR ABOUT 2 MINS AND ONLY AFTER I QUESTIONED HIM DID HE DIVULGE THAT MY FINAL WT CALCULATIONS WERE WRONG. WHILE IN THE PROCESS OF RECALCULATING THE WTS; WE WERE CLRED FOR TKOF. THE CAPT ASKED IF THE TKOF WT AND SPDS WERE NOW CORRECT. THE WT WAS NOW CORRECT WITH NO CHANGE IN THE ORIGINALLY COMPUTED SPDS. BUT I HAD YET TO FINISH THE LNDG WT AND DECLINED THE TKOF CLRNC UNTIL I WAS SURE THAT ALL WTS WERE CORRECT. BEING RUSHED IS NO EXCUSE; ESPECIALLY WHEN THE FAA IS ON BOARD. I SHOULD HAVE USED A CLEAN WT AND BAL SHEET INSTEAD OF ADDING THE 170 LBS OVER THE OTHER WTS.