What was found
AIRCRAFT LEVEL AT 15,000FT, ATC SHOWED ALTITTUDE READOUT OF 22,700FT. AFTER DESCENT FROM 15,000FT ATC BEGAN TO SEE NORMAL ALTITTUDE READOUT. AIRCRAFT RETURNED TO MX BASE WITHOUT INCIDENT FOR REPAIRS. NO EMERGENCY ACTION WAS REQUIRED. AFFECTED SYSTEM BEING TROUBLESOT AT THIS TIME.