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Precise and accurate internal-combustion engine pressure measurements are typically built upon extremely low level piezoelectric sensor signals acquired in the laboratory. In turn, these minute signals must be accurately conditioned using electronic charge amplifiers and then processed for meaningful analysis. Laboratory standard operating procedures often overlook the importance of timely and rigorous calibration of the equipment, or perform them without using sufficient environmental controls. In some facilities, years have been allowed to pass between metrology-quality calibrations, introducing the potential for significant out-of-tolerance conditions and non-compliance when compared to accredited measurement standards. Environmental, aging and operator factors influencing calibration metrology and in-use accuracy are presented in this paper, along with a method and example for estimating the calibration interval needed to specify calibration frequency for charge amplifiers.