What was found
WHILE BURNING OUT OF CENTER TANK, STARTED NOTICING SLOW DECREASE IN NR 2 MAIN TANK QTY FUEL MONITORING INDICATED LOSS OF 1300 LBS BETWEEN 2 WAYPOINTS 1.5 THIS CORRESPONDS WITH WHAT WE SAW ON THE NR 2 FUEL GAUGE DECISION WAS MADE TO RETURN TO DEPARTURE, BY THE TIME WE LANDED THE PROBLEM SELF CORRECTED SUSPECT UNRELIABLE NR 2 FUEL GAUGE. TOTAL FUEL USED FINAL QTY. AGREED WITH DEP FUEL. ACFT GROUNDED. DIVERSION TIME, 99 MINUTES. PERFORMED VENT AND DRAIN INSPECTION ON BOTH ENGINES IAW AMM 71-71-00. NO LEAKS WERE NOTED. PERFORMED FQIS BITE TEST IAW FIM 28-41, TASK 801 NO FAULS NOTED GROUND TEST PASS. PERFORMED FUEL SUMPING ON ALL TANKS SUMP CKECKS GOOD PERFORMED FQIS WITH FUEL STICK COMPARRISON CHECK GOOD, ACFT OK FOR SERVICE.