What was found
FUEL QTY AT PREFLIGHT WAS 20.2 AT PUSH BACK FUEL QTY WAS 19.2 THE APU WAS ON FOR A TIME PERIOD OF 20 MIN FUEL GAUGE NR 1 & NR 2 WENT BLANK FOR ABOUT 5 SECONDS, RESPECTIVELY AT DIFFERENT TIME. ALL 3 FUEL GAUGE READINGS HAVE REDUCE FROM ORIGINAL READING. ACFT GROUNDED. FOR ALL INSPECTION, POWER REMOVAL REQUIREMENTS, AND LEAK CHECKS REF TANK ENTRY PERMIT W/C 78528000. R & R NR 1 FUEL QUANTITY COMP PROBE REF MM 28-41-21. OPS NORMAL.