A CL600 WAS FLOWN ON TWO FLIGHTS WITH AN INCORRECT WEIGHT AND BALANCE. THE CALCULATIONS WERE OFF BY 20 UNITS BECAUSE OF AN INCORRECT WEIGHING.

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WHILE ACTING AS PIC; MY FO AND I INADVERTENTLY FLEW 2 FLTS WITH INCORRECT WT AND BAL DATA. THE PROB AROSE DUE TO THE FACT THAT THE OFFICIAL WT AND BAL DATA WAS INCORRECTLY CALCULATED DURING THE ACFT'S LAST WEIGHING AND; UNBEKNOWNST TO US; SHOWED A BALANCE INDEX THAT WAS OFF BY ABOUT 20 UNITS. DURING THE FIRST FLT; WE REQUIRED BALLAST IN ORDER TO BRING THE ACFT INTO TRIM RANGE; BUT THIS IN ITSELF IS NOT UNCOMMON. IT WAS THE FACT THAT FOR THE RETURN TRIP WE AGAIN REQUIRED BALLAST THAT I CONTACTED THE COMPANY'S MAINT CTL AND WAS ADVISED THAT THE OFFICIAL WT AND BAL DATA IN THEIR RECORDS MATCHED THE DATA IN OUR ACFT LOG; AND THAT IT WAS; THEREFORE; CORRECT. AT THIS POINT; I NOTICED THAT THE BALANCE INDEX WAS ABOUT 55 INSTEAD OF THE USUAL LOW 70'S AND; THEREFORE; OBVIOUSLY NOT CORRECT. HAVING POINTED THIS OUT; MAINT AGREED TO CONTACT THE WEIGHING FACILITY AND ASK THEM TO RE-CHK THE DATA. ADVISED THE NEXT FLT CREW OF THE SITUATION. AS I AM UNFAMILIAR WITH WEIGHING PROCS; I CANNOT COMMENT ON HOW TO AVOID SUCH MISTAKES IN THE FUTURE; EXCEPT THAT PERHAPS WHEN NEW AND OLD WT AND BAL DIFFER BY A CERTAIN AMOUNT THAT THERE AUTOMATICALLY NEEDS TO BE A RECALCULATION AND ALSO AN EXPLANATION OF THE CHANGE.