GOV-LTT OVERSHOT ALT ON CLIMB RESULTING IN LESS THAN STANDARD SEPARATION WITH ACR-LTT.

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DURING A ROUTINE RESEARCH FLT TO R5503 NEAR DAYTON; OH; I WAS CLRED TO FL190 AND ASKED TO EXPEDITE THROUGH FL180. LEVEL OFF WAS ATTEMPTED NEAR THE TOPS OF EXISTING CLOUDS AND UNDER TURBULENT CONDITIONS. ALTIMETER EXCURSIONS WERE PRESENT DURING THE LEVEL OFF SEQUENCE DUE TO THE EXISTING TURB AND FOR A MOMENT INDICATED 19300'. THIS CONDITION WAS IMMEDIATELY CORRECTED AND SHORTLY THEREAFTER WE WERE ASKED TO VERIFY OUR ALT. AT THIS POINT CORRECTIVE ACTIONS HAD BEEN INITIATED AND THE COPLT RESPONDED THAT WE WERE CORRECTING BACK TO THE ASSIGNED ALT. DURING THE LEVEL OFF; CONSIDERATION WAS GIVEN TO NOT SUBJECTING THE ACFT TO NEGATIVE 'G' FORCE CONDITIONS DUE TO THE NATURE OF THE ONBOARD EXPERIMENT THAT CONSISTED OF A CAREFULLY PLACED BEAD OF LYCOPODIUM POWDER ON THE BOTTOM OF A HORIZ FLAME TUBE. PRIOR DISPLACEMENT OF THE POWDER WOULD HAVE RENDERED THE EXPERIMENT INVALID. CONSIDERATION WAS ALSO GIVE TO THE COMFORT OF 2 RESEARCH ENGINEERS ON BOARD. FOLLOWING THE REQUEST TO VERIFY OUR ALT; WE WERE SUBSEQUENTLY GIVEN A TFC ADVISORY OF ANOTHER ACFT AT FL200 AND OUR 6 O'CLOCK POS WHICH WE APPARENTLY HAD PASSED DURING THE COURSE OF EVENTS FOLLOWING LEVEL OFF. ALTHOUGH THE ALTIMETER DID INDICATE 19300' MOMENTARILY; THE ACFT IN ALL PROBABILITY DID NOT REACH THAT ALT BECAUSE OF THE STATIC ERROR PRESENT IN THE ACFT; WHICH RESULTS IN AN ALT INCREASE DURING A PUSH OVER AND A DECREASE DURING PULL UP. DEPENDING ON THE SEVERITY OF THE PUSHOVER/PULL UP; ALTIMETER EXCURSIONS OF 100-200' ARE COMMON.