FLC OF ACR MLG OVERSHOT XING ALT RESTR DUE TO NOT SETTING THE ALTIMETERS TO CURRENT SETTING.

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ON THE GARDNER 2 ARR INTO BOS WE WERE GIVEN 'CROSS BRONC 11000 FT AND 250 KIAS.' I WAS THE PF. IN THE DSCNT AT ABOUT 22500 FT AND DSNDING; THE CAPT TELLS ME HE'S GOING TO LEAVE THE COCKPIT FOR A QUICK BREAK. I THINK; 'THIS IS NOT A GOOD TIME;' BUT AS WE'RE JUST RECENTLY MET AND I CAN'T THINK OF A QUICK AND TACTFUL WAY TO STATE DISAPPROVAL; I'M QUIET. SO I'M DSNDING TO MAKE THE XING RESTR AND MONITORING THE BUSY ATC FREQ AND DOING THE DSCNT CHKLIST THROUGH 18000 FT AND TUGGING AT MY ALTIMETER BUTTON AND HIS ALTIMETER BUTTON AND RESETTING THE STANDBY BAROMETER ALTIMETER TO MATCH THE OTHERS (THAT WAS TUGGING THE ALTIMETER RESET BUTTONS ONLY; NOT RESETTING TO THE PROPER SETTING!) I LEVELED OFF AT WHAT I THOUGHT WAS 11000 FT; 250 KIAS AT BRONC. THE CTLR SAID 'BOSTON ALTIMETER 29.92' (OR 29.91) AND I READ IT BACK CONFIRMING THE PROPER SETTING WRITTEN DOWN ON MY ATIS FORM AND STILL NOT CATCHING MY ERROR. I BELIEVE BECAUSE THERE WASN'T A CHALLENGE AND RESPONSE OF THE DSCNT CHK AT 18000 FT I WASN'T MENTALLY BELOW 18000 FT. A MIN OR 2 LATER; THE CAPT RETURNED; THEN I CAUGHT MY ERROR AND WE FOUND ALL 3 ALTIMETERS SET TO THE DEP SETTING OF 30.17 INSTEAD OF THE BOS ARR SETTING 29.92. WE SET ALL 3 ALTIMETERS TO THE CORRECT SETTING. THE ACFT WAS 200-300 FT LOW. WE EASED THE ACFT BACK TO 11000 FT. NOTHING WAS SAID AND THE REST OF THE FLT WAS NORMAL. (IT TAKE 2 OR MORE WHEN THINGS GET BUSY!)