What was found
RED MAG FLAG APPEARED ON FO'S INSTRUMENTS WHILE IN POSITION FOR TAKEOFF., DECLINED TAKE OFF CLEARANCE, NO THRUST, 0 KNOTS, FLAG CLEARED AFTER EXITING RUNWAY. PERFORMED OPS TESTS OF ATTITUDE AND HEADING COMPUTER IAW AMM 34-21-01. OPS TEST GOOD AT THIS TIME. NO FAULTS NOTED AT THIS TIME.