ALTDEV ALT OVERSHOT ON DSCNT DUE TO WRONG ALTIMETER SETTING.

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APCHING THE HBU VOR FROM THE SE; WE SENT AN AWOS RPTED ALTIMETER SETTING OF 29.77 THROUGH ACARS TO OUR ACR TO GET THE KOLLSMAN CONVERSION TO SET BOTH PLT'S ALTIMETERS TO QFE FOR APCH AND LNDG. APPARENTLY AN ERROR WAS MADE WHEN WE PUT THE NUMBERS INTO OUR ACARS SENDING UNIT; AND 29.22 WAS SENT. THE CONVERSION SETTING WAS MADE BY ACR COMPUTER; AND BOTH NUMBERS WERE RETURNED TO US ON THE ACARS PRINTER AT 29.22 QNH AND 21.99 QFE. THIS SHOWED A DIFFERENCE BTWN THE 2 PLT'S ALTIMETERS AND THE THIRD ALTIMETER EQUAL TO GUC FIELD ELEVATION; OUR NORMAL PROC FOR XCHKING THE ALTIMETERS. WE DSNDED TO 16000 AS WE CROSSED HBU AND STARTED TO FOLLOW THE 14 DME ARC W TO INTERCEPT THE LOC FOR AN ILS APCH TO RWY 6; CIRCLE TO 24. ZDV THEN GAVE US ANOTHER ALTIMETER SETTING OF 29.77. WE THEN REALIZED SOMETHING WAS WRONG; AND WHEN THE CTR ALTIMETER WAS RESET TO 29.77; IT SHOWED US ABOUT 500 FT LOW. WE IMMEDIATELY CLBED BACK UP TO 16000 AT ABOUT THE TIME ZDV ASKED WHAT OUR ALT WAS. BY NOW WE ARE PASSING THE 200 DEG OR 220 DEG RADIAL OF HBU ON THE 14 DME ARC. WE KNEW NOW THAT THE DIFFERENCE BTWN ALTIMETERS DID NOT EQUAL FIELD ELEVATION; BUT WE COULD NOT GET A NEW QFE THROUGH ACARS BEFORE WE BROKE THROUGH THE SCATTERED CLOUDS AND HAD THE FIELD IN SIGHT FOR THE CIRCLE AND LNDG. THE PROBLEM CAME FROM OUR INPUT ERROR AND THEN NOT REALIZING THAT 29.22 COULD NOT BE CORRECT; EVEN IN AN AREA WHERE LOW BAROMETER IS NOT TOO UNUSUAL. WE ALSO SHOULD HAVE GOTTEN THE ALTIMETERS SET AND CHKED SOONER BEFORE BEGINNING AN UNUSUALLY BUSY APCH EVEN WHEN EVERYTHING GOES SMOOTHLY.