MD80 FLC OVERSHOOT ASSIGNED ALT ON DEP WHEN BOTH PLTS ATTEMPT TO TROUBLESHOOT COMPASS SYS SPLIT.

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BOTH COMPASS SYS SPLIT ON INITIAL TURN TO HDG OF 190 DEGS. DIVERGENCE INCREASED RADICALLY ON TURN TO 220 DEGS AT 2.3 MI DME. ATTN DIVERTED TO STANDBY COMPASS TO CONFIRM ACTUAL HDG. EXCEEDED ASSIGNED ALT OF 2500 FT BY APPROX 600 FT. RETURNED TO 2500 FT EXPEDITIOUSLY AND CONTINUED TO WORK COMPASS PROB. IN RETROSPECT; I INAPPROPRIATELY DEVOTED TOO MUCH ATTN TO THE ABNORMAL CONDITION RATHER THAN MAINTAINING MORE COMPREHENSIVE SITUATIONAL AWARENESS. ADDITIONALLY; THE STANDBY COMPASS ON THE DC9/MD80 IS ABYSMAL. IT IS AN AWKWARD ARRANGEMENT; AT BEST. THE COMPASS MUST BE VIEWED THROUGH A SYS OF MIRRORS WHICH EASILY GET OUT OF ALIGNMENT. THE MONITORING PLT WAS REMOVED FROM HIS 'MONITORING ROLE' BY THE IMMEDIATE NEED TO REALIGN THE MIRRORS OF THE STANDBY COMPASS. SUPPLEMENTAL INFO FROM ACN 510481: WE HAD A COMPASS DISCREPANCY. I ATTEMPTED TO CONFIRM OUR HDG BY USING THE MAGNETIC COMPASS AND XCHKING WITH BOTH COMPASS SYS. THIS IS ACCOMPLISHED ON THE MD80 WITH A SERIES OF MIRRORS AND LIGHTS. THE CAPT WAS FLYING THE ACFT. A FEW SECONDS LATER; I HEARD THE ALT RPTR NOTIFY US OF A DEV. I FEEL I COULD HAVE MONITORED THE ACFT BETTER; HAD I NOT BEEN TRYING TO FIND THE COMPASS IN THE BACK OF THE COCKPIT THROUGH THE SERIES OF MIRRORS.