A CL65 CREW; ON DSCNT INTO CVG; OVERSHOT A STAR XING RESTR.

Narrative

WE WERE DSNDING ON THE CINCE FOUR ARR INTO CVG. DSNDING THROUGH FL180 WE SET THE ALTIMETERS TO 29.72; THE LCL ALTIMETER SETTING GIVEN TO US BY THE CTR CTLR. WE PERFORMED THE DSCNT CHKLIST AND THE CAPT VERBALLY CONFIRMED THE ALTIMETER SETTING PER THE CHKLIST. WE WERE THEN CLRED TO DSND TO 8000 FT. I WAS SETTING UP FOR THE APCH AND LOOKED UP AT THE INSTS AND NOTICED MY ALTIMETER WAS SHOWING US DSNDING THROUGH 7300 FT. I IMMEDIATELY CALLED OUT WE WERE ASSIGNED 8000 FT TO THE CAPT; AND NOTICED HIS ALTIMETER READ 8300 FT. WE DETERMINED HIS ALTIMETER HAD CHANGED TO 30.72; RESET IT TO THE CORRECT SETTING OF 29.72 AND BEGAN A CLB BACK TO 8000 FT. AS WE WERE LEVELING AT 8000 FT CTR ASKED US ABOUT OUR ALT. WE CONFIRMED WE WERE LOW AND CORRECTING. THERE WERE NO TFC CONFLICTS DURING THE ALTDEV. THE INCORRECT ALTIMETER SETTING CAUSED A 1000 FT DIFFERENCE BTWN THE 2 ALTIMETERS. I DO NOT KNOW HOW OR WHY THE ALTIMETER SETTING CHANGED. THE ONLY WAY I CAN THINK OF TO AVOID THIS SIT IN THE FUTURE IS TO HAVE AN ALTIMETER SETTING COMPARATOR TO WARN OF A DIFFERENCE BTWN 2 ALTIMETERS.