What was found
AIRCRAFT WAS NOT GROUNDED: FUEL DISAGREE EICAS MESSAGE DIFFERENCE DISPLAYED BETWEEN TOTALIZER AND CALCULATED INCREASE FROM 6.7 TO 9.7 OVER APPROXIMATELY 40 MINUTES. ACCOMPLISHED QRH PROCEDURE, SUSPECTED CENTER TANK FUEL LEAK. AFTER ALL CENTER TANK FUEL WAS USED, DIFERENCE REMAINED STABLE OVER DURATION OF FLIGHT, VERY SLOWLY INCREASING FROM 9.7 TO 11.0 . NO LEFT TO RIGHT FUEL IMBALANCE. MAINTENANCE ACCOMPLISHED FIM TASK 28-41-00, NO FAULTS NOTED.