FLT CREW SCHEDULING PRACTICES AND FATIGUE CONTRIBUTE TO MISSET ALTIMETER AND ALTDEV FOR CARJ.

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LCL ALTIMETER SETTING WAS 30.42. MY ALTIMETER AND STANDBY WERE SET TO 30.42. THE CAPT INADVERTENTLY SET 29.42. HE WAS THE PF; AND THE FCP/FD WAS SELECTED TO HIS SIDE. WE WERE CLRED TO 4000 FT; AND THE ACFT ON AUTOPLT CONTINUED TO DSND TO 3000 FT (4000 FT ON THE CAPT'S DISPLAY). BEFORE WE REALIZED THIS ERROR; WE HAD DSNDED 1000 FT BELOW OUR CLRNC. HIS DISPLAY SHOWED US AT 4000 FT; AND MINE INDICATED 3000 FT. AS SOON AS I RECOGNIZED THIS INCONGRUENCE; I QUERIED ATC'S LCL ALTIMETER SETTING. THEY SAID '30.42 AND YOU CAN REMAIN AT 3000.' I APOLOGIZED; AND ATC RESPONDED THAT IT WASN'T A PROB. THE CAPT WAS NOTICEABLY WORN OUT FROM MANY DAYS AND MONTHS OF HVY RESERVE DUTY. I FLEW WITH HIM A YR AGO; AND HE WAS A MUCH DIFFERENT CAPT THEN. HE USED TO BE VERY ALERT AND RESPONSIBLE. A YR LATER; HE IS STILL ON RESERVE WITH MAX FLYING; MINIMUM REST; AND MINIMUM DAYS OFF. HE IS ALMOST TO THE POINT OF DISAFFECTION WHEN IT COMES TO HIS JOB. THIS IS A COMMON PROB AT MY AIRLINE. WE ARE STRETCHED TO THE MAX FLYING ALLOWED BY THE FAR'S ON A DAILY; WEEKLY; AND MONTHLY BASIS; THEN WE ARE REGULARLY REDUCED TO ABSOLUTE MINIMUM REST AND DAYS OFF (FREQUENTLY REDUCED TO 8 HRS REST; AND REGULARLY FLYING 6 DAYS ON AND 1 OFF). WE ARE TOO SHORT STAFFED AND OUR SCHEDULES ARE TOO DEMANDING TO ALLOW FOR ADEQUATE REST AND MAX PERFORMANCE. I BELIEVE FATIGUE; IN GENERAL; WAS A MAIN FACTOR CONTRIBUTING TO THE AFOREMENTIONED INCIDENT. ALSO; I SHOULD HAVE BEEN MORE AWARE AND FASTIDIOUS OF THE SITUATION BEFORE WE DSNDED AS FAR AS WE DID. I SCAN FREQUENTLY AS THE PNF; BUT I DID NOT EXPECT THE CAPT TO MAKE SUCH AN EASY; YET POSSIBLY DEADLY; MISTAKE.