What was found
ON ROTATION THE FIRST OFFICERS ALTIMETER DESCENDED TWO THOUSAND FEET (-2000). ALTIMETER REMAINED 2000 FT BELOW THE CAPT'S ALT AND STANDBY ALT REMAINDER OF FLIGHT. SWITCHED CADC'S, NO CHANGE - ALT STATIC SOURCE NO CHANGE. REMOVED AND REPLACED NR 2 AIR DATA COMPUTER IAW DC10-10 AMM 34-16-01-2. NR 2 ALTIMETER SYSTEM OPERATIONAL CHECKS NORMAL, NO DISCREPANCIES NOTED. PREMATURE REMOVAL/INSTALLATION, OFF MFG HG280D4, POS P2 SRL 465, TAG A03096, ON MFG HG280D80 SRL 115, TAG 590682.