ACFT WT AND BAL COMPUTATIONS IN ERROR DUE TO HANDHELD COMPUTERS BEING INOP.

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OUR COMPANY USES A STANDARD MANIFEST FORM FOR CALCULATION OF WT AND BAL. WE USE A HANDHELD SCIENTIFIC CALCULATOR WHICH HAS BEEN PROGRAMMED TO DO THE CALCULATIONS. AS DATA IS ENTERED (TEMP; PRESSURE ALT; FUEL; ETC) THE PROGRAM PROMPTS THE USER TO ENTER THE NEXT PIECE OF DATA. ON THIS DATE; THE CALCULATOR BATTERY APPEARED TO BE DEAD; AND THE CALCULATOR DID NOT WORK. OPS HAD NO EXTRA CALCULATORS OR BATTERIES; SO I PROCEEDED TO PREPARE THE MANIFEST USING A REGULAR CALCULATOR; AND LOOKING UP MOMENTS IN THE P.O.H. IT HAD BEEN QUITE A WHILE SINCE I HAD DONE ONE OF OUR MANIFESTS MANUALLY. I COMPLETED THE MANIFEST IN MKE; AND ALSO DID MANUAL MANIFESTS IN FNT FOR OUR LEG TO LAN; AND IN LAN FOR OUR LEG TO MKE. WHILE I WAS UNCOMFORTABLE DOING THE CALCULATIONS MANUALLY; THE NUMBERS SEEMED REASONABLE; BASED UPON MY EXPERIENCE; FOR THE LOADS WE HAD ON BOARD. THAT EVENING I WORKED THROUGH THE MANIFESTS AGAIN TO VERIFY THEIR ACCURACY. I FOUND THAT THEY WERE NOT CORRECT; AS I HAD MIXED MOMENTS AND CTR OF GRAVITY IN THE CALCULATION. NONE OF MY FLTS WERE OUT OF THE APPROVED CTR OF GRAVITY RANGE; BUT THEY COULD HAVE BEEN SINCE I HAD DONE THE CALCULATIONS WRONG. CONTRIBUTING FACTORS/AREAS FOR IMPROVEMENT: I; AS PIC; NEED TO MAKE SURE I AM UP TO DATE ON DOING MANIFESTS MANUALLY. OUR MANIFEST FORMS (SEE COPY ATTACHED); HAS THE ACFT CTR OF GRAVITY IN THE MOMENT COLUMN; RESULTING IN THE POTENTIAL FOR MIXING CTR OF GRAVITY AND MOMENTS. THE P.O.H.; AND OUR MANIFEST; USE DIFFERING MOMENTS (STRAIGHT MOMENT; MOMENT/100; MOMENT/1000; ETC). IT SHOULD BE VERY CLR (I.E.; MARKED) ON A MANIFEST WHAT MOMENT IS BEING USED. IT SHOULD ACTUALLY SAY 'ARM/100' OR 'MOMENT/100'. I'VE LEARNED MY LESSON AND WILL ALWAYS KEEP UP TO DATE ON MY ABILITY TO DO MANIFESTS MANUALLY.