WRONG ALTIMETER SETTING CLBING THROUGH 18000 FT; CAPT SET 30.92 INSTEAD OF 29.92. THUS; LEVELED 1000 FT TOO LOW. ATC ISSUED NEW CLRNC.

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WE WERE CLRED TO FL250 ENRTE FROM PIT TO PHL. CLBING THROUGH 18000 FT MSL; I CALLED FOR ALTIMETERS TO BE RESET FROM 30.83 TO 29.92. I RESET MY ALTIMETER AND THE ALT ALERTER TO 29.92 AND HEARD THE CAPT ACKNOWLEDGE THE CHANGE IN SETTING; HOWEVER; I DID NOT WITNESS THE ACTION. I THEN BEGAN MAKING ROUTINE FLT FOLLOWING RADIO CALLS AND MAKING ENTRIES TO OUR LOG/PAY SHEET AND WAS ESSENTIALLY 'OUT OF THE LOOP.' THE CAPT LEVELED OFF AT HIS ALTIMETER INDICATION OF FL250; YET NEITHER OF US HEARD OR SAW THE AURAL/VISUAL ALT ALERTER INDICATION OF APCHING ALT. AFTER SEVERAL MINS AT CRUISE; ARTCC INQUIRED OF OUR ALT; TO WHICH I RESPONDED FL250 (WITHOUT VERIFYING VISUALLY). ARTCC SAID HE SHOWED FL241. WHEN I XCHKED MY ALT AGAINST THE CAPT'S; I INDICATED FL240 WHILE HIS WAS FL250. I ASSUMED MY ALTIMETER HAD AN ERROR. AFTER CAREFULLY OBSERVING HIS ALTIMETER SETTING; I DISCOVERED THE ERROR - - HE HAD MISSET HIS ALTIMETER TO 30.92 INSTEAD OF 29.92; THEREBY CAUSING HIS TO INDICATE 1000 FT HIGHER. WE IMMEDIATELY ASKED FOR AND WERE APPROVED FOR FL240. NO CONFLICTS OCCURRED. I'VE LEARNED TWO VERY IMPORTANT LESSONS: FIRST; ALWAYS XCHK PF/PNF FLT INSTS/ALTIMETER SETTINGS; AND SECOND; ALWAYS STAY 'IN THE LOOP' MAINTAINING SITUATIONAL AWARENESS -- ESPECIALLY WHEN APCHING ASSIGNED ALTS. PAPERWORK AND OTHER NON ESSENTIAL DUTIES CAN WAIT.