What was found
ENROUTE, BOTH ALTIMETERS SHOWED LEVEL AT FL350 ATC STATED THE RETURN WAS SHOWING 400' HIGH. TRANSPONDER WAS SELECTED NR 1. PERFORMED TEST ON NR 1 & 2 TRANSPONDERS REF MM 34-54-001-2 NO FAULTS FOUND. PERFORMED SELF TESTS ON ADDU AND CADC REF MM 34-12-001-5-02 NO FAULTS FOUND. TESTED ALTITUDE ALERT SYSTEM REF 34-17-00-5 - NO FAULTS FOUND. IAW FIG 201 MM 34-10-00-2-0 ALL ACFT REQ RVSM SYSTEMS WORKING NORMAL. ACFT HAS NO HISTORY OF ALT PROBLEMS FOR PAST 99 DAYS. A/C OK FOR SERVICE.