What was found
APPROX 1.5 HRS INTO FLIGHT, RT OTBD FUEL TANK QTY BEGAN TO DECREASE RAPIDLY. TANK WENT TO EMPTY, XX, AND REMAINED UNTIL IN DESCENT AT 16,000 FT, THEN QTY RETURNED TO 6.42. TROUBLESHOOTING VERIFIED FUEL LEVEL IN RT OTBD TANK ON RT NR 2 & NR 3 MAGNETIC LEVEL INDICATORS IAW AMM 12-11-28-3. RESET FUEL QUANTITY COMPUTER OPS CHECKED GOOD IAW AMM 28-42-38-5. ACFT IS OK TO CONTINUE.