B737-700 FLT CREW UTILIZES AN INCORRECT ALTIMETER SETTING ON DESCENT.

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WE PREPARED FOR THE DSCNT BY OBTAINING THE D-ATIS (DIGITAL ATIS); CONSULTING THE PERFORMANCE INFO; AND COMPLETING THE ARR BRIEFING PRIOR TO DSCNT. DURING THE APCH; THE FO NOTICED A DISCREPANCY BTWN THE RA ALTS AND THE ALTIMETER READINGS AND REQUESTED THE CURRENT ALTIMETER FROM TWR. WE HAD SET 30.04 PASSING FL180 WHICH WAS TRANSCRIBED ON THE NAPKIN. THE ALTIMETER THAT TWR GAVE WAS 30.33. AT THE GATE; I CHKED THE D-ATIS THAT WE HAD REFED IN THE FMC AND IT READ 30.34. THE FO HAD WRITTEN THE INCORRECT ALTIMETER SETTING ON THE NAPKIN AND MY BRIEF WAS BASED ON THAT NUMBER. THE RNAV ARR WAS FLOWN PRECISELY BUT WITH THE INCORRECT ALTIMETER SETTING FROM FL180 AND BELOW. THE SACCO; FIMBO; UDUDE; REXEE; OTT; AND RAVNN XING RESTRS WOULD HAVE BEEN AFFECTED. I CAN CORRECT THIS TYPE OF ERROR IN THE FUTURE BY PULLING UP THE D-ATIS ON THE FMC AS I DO THE DSCNT CHKLIST; BUT WE ARE USUALLY ACTIVE IN THE DSCNT SO THE DSCNT PAGE IS BEING UTILIZED. THERE WERE NO UPDATES ISSUED BY APCH NOR WAS AN ALTIMETER GIVEN WHEN WE WERE ASSIGNED TO DSND VIA THE RAVNN2 ARR AS WE CHKED IN WITH THE D-ATIS FROM BWI. A QUICK BUTTON TO PULL UP THE D-ATIS IN THE FMC WOULD ALLOW CREW MEMBERS TO REF THE ARR INFO DIRECTLY TO CIRCUMVENT TRANSCRIPTION ERRORS WITHOUT HAVING TO GO THROUGH 3-4 PAGES TO ACCESS THE DATA AS IS REQUIRED NOW.