CARJ FLC; DEPARTING PHX; MADE A MISTAKE ON THE WT AND BAL MANIFEST; PUTTING THEM OUT OF CTR OF GRAVITY LIMITS.

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OUR FLT WAS MISLOADED WITH TOO MANY BAGS PRIOR TO DEP. WE CALCULATED HOW MANY BAGS WE COULD TAKE AND TOLD OUR GND AGENTS TO REMOVE 49 BAGS. AS WE WORKED TO GET AS MANY BAGS AS WE COULD ON BOARD WHILE BEING CAREFUL TO NOT BE OVERWT; MY FO INADVERTENTLY MADE A MISTAKE ON OUR WT AND BAL MANIFEST. RATHER THAN ROUNDING DOWN 825 LBS TO 800; WHICH WOULD HAVE BEEN THE CORRECT PROC; HE INCLUDED THE 25 LBS INTO THE ADJUSTED WT UNIT; MAKING IT 825.8 WHEN IT SHOULD HAVE BEEN 805.8. THE PROB IS THAT THE LAST 3 DIGITS ARE AN INDEX; NOT WT. WHEN HE FINISHED THE WT AND BAL MANIFEST; HE GAVE IT TO ME TO SIGN. I REVIEWED IT AND DID NOT NOTICE THE ERROR. AS A RESULT; OUR ZERO FUEL WT INDEX WAS PLOTTED 20 UNITS AFT OF WHERE IT ACTUALLY SHOULD HAVE BEEN; AS WAS THE GROSS TKOF WT. THE NET RESULT WAS WE APPEARED TO BE WELL WITHIN OUR ZERO FUEL AND TKOF ENVELOPES; BUT WERE ACTUALLY 2 UNITS IN FRONT OF THE FORWARD ZERO FUEL INDEX LIMIT AND 1 UNIT FORWARD OF THE GROSS TKOF WT INDEX LIMIT. WE TOOK OFF THIS WAY AND WITH THE EXCEPTION OF HAVING OUR PITCH TRIM SET FOR THE WRONG CTR OF GRAVITY INDEX THE FLT PROCEEDED UNEVENTFULLY TO ITS DEST. THE PROB MAY HAVE BEEN AVOIDED WITH BETTER (MORE) TRAINING IN GND SCHOOLS ABOUT THE WT AND BAL MANIFEST AND IF I FLEW MORE OFTEN; I MAY HAVE NOTICED THE MISTAKE PRIOR TO DEP.