CAPT OF AN LTT PERSONAL JET SET THE ALTIMETER WITH THE WRONG SETTING RESULTING IN AN OVERSHOOT ON DSCNT. THE FO NOTICED THE CAPT'S MISTAKE AND THE CAPT CORRECTED BACK AFTER OVERSHOOTING 600 FT.

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DSCNT CLRNC WAS RECEIVED TO 17000 FT AT FL180. THE PNF CALLED THE ALTIMETER SETTING ABOUT 200 FT PRIOR TO FL180. THE PF HEARD THE SETTING AT 30.36 WHEN IT WAS ACTUALLY 29.36. CORRECTED BY THE PNF IMMEDIATELY. THE MOMENTUM OF THE DSCNT CARRIED THE ACFT THROUGH THE ALT SINCE DSCNT WAS EXPECTED TO CONTINUE BY PF. TO COMPLICATE MATTERS; THE MISSETTING OF THE ALTIMETER HAD TO BE REVISED TO SEE WHERE THE ALT WAS IN ORDER TO CORRECT THE ERROR. AS A RESULT OF THE TIME INVOLVED; THE ACFT VENTURED THROUGH THE ASSIGNED ALT. CORRECTIVE ACTION WAS IMMEDIATELY TAKEN AND CORRECTION WAS NO MORE THAN 3-5 SECONDS. CREW HAD BEEN ON DUTY FOR 11 1/2 HRS -- THE LAST LEG BEGIN 4 HRS 20 MINS. THE NOSE LEVEL OF THE ACFT IS HIGH AND CREW FATIGUES MORE READILY. THE CREW IS WEST COAST BASED AND WAS GENERALLY TIRED DUE TO EARLY MORNING EAST COAST OPS FOR THE PREVIOUS 3 DAYS. NORMAL OPS REQUIRE SETTING THE ALTIMETER SO AS TO PASS THROUGH FL180 ON THE LCL ALTIMETER. IN THIS CASE; APPROX 600 FT PRIOR WOULD HAVE BEEN APPROPRIATE. A CLASSIC CASE OF HEARING WHAT WAS TO BE EXPECTED WHILE SOMEWHAT FATIGUED. FORTUNATELY CREW COORD AND GOOD COCKPIT PROCS PREVENTED AN UNFORTUNATE SIT FROM BECOMING A VERY BAD ONE.