As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING FLIGHT FROM ORD, CAPTAIN`S ALTIMETER JUMPED ERRATICALLY BETWEEN 22.00 - 32.00. UNABLE TO RESET WITH BARO KNOB TO PROPER SETTING. DIVERT TO CAK. REMOVED AND REPLACED NR 1 ADC IAW AMM 34-11-00. OPERATIONAL CHECK GOOD. A/C REMAINS CAT II & RVSM.