A CL65 PIC DELAYS HIS RESETTING OF HIS ALTIMETER UNTIL 16500 FT. UPON SETTING THE 29 PT 29 FROM 29 PT 92 HE FINDS THAT HE HAS OVERSHOT HIS ASSIGNED ALT OF 16000 FT BY 300 FT; 80 MI SW OF LGA; NY.

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WE HAD BEGAN OUR DSCNT ALONG THE STAR INTO LGA FROM THE W. AT FL180; WE SHOULD HAVE RAN OUR CHKLIST TO RESET OUR ALTIMETERS FROM 29.92 TO LCL SETTING OF APPROX 29.29. THE FO WAS BUSY WITH ATIS; COMPANY RADIO; ETC; AND I WAS THE PF DSNDING TO OUR ASSIGNED ALT OF 16000 FT MSL. AT APPROX 16500 FT MSL (WITH 29.92 AS REF ALTIMETER SETTING) I ENTERED IN LCL ALTIMETER SETTING OF 29.29. I NOTICED UPON RESETTING THIS NEW; LCL ALTIMETER SETTING THAT OUR ACTUAL ALT WAS APPROX 15700 FT. I IMMEDIATELY ARRESTED THE REMAINDER OF OUR DSCNT RATE; REVERSED OUR ACFT'S TREND AND IMMEDIATELY CLBED BACK TO 16000 FT MSL. ATC HAD INQUIRED ABOUT OUR ALT AND OFFERED THE LCL ALTIMETER SETTING. NO CONFLICT OR OTHER CONVERSATION ABOUT THIS DISCREPANCY. I REALIZE THE TIMELINESS OF COMPLETING CHKLISTS AT THE TIME THEY SHOULD BE COMPLETED. WITH SUCH A LOW ALTIMETER SETTING THIS DAY; THIS EVENT WAS JUST 'ITCHING TO OCCUR.' THE ONLY REASON THESE CHKLISTS SHOULD BE HELD IS FOR RADIO XMISSIONS; ETC. THEY SHOULD THEN BE COMPLETED ASAP THEREAFTER.