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Instrument calibration involves determining the difference (if any) between the output reading produced and a known standard, and remedying that difference. For digital scales, this means ensuring that the microprocessor correctly relates the amplified digital output signal to a standard weight. Manufacturers of the digital scales most commonly used by firearms examiners provide both known weights (usually not NIST traceable) and detailed but simple instructions for calibration. Calibration takes only a few minutes to perform but is necessary to ensure the accuracy of results.
Changes in heat and humidity as well as unlevel working surfaces can affect the readings of a digital scale by slightly shifting the zero point. Rough usage and power surges can cause harm to a digital scale.
Calibration of a digital scale is simple to perform. However, NIST traceable weights for calibration are a requirement of ISO/IEC 17025:2005 accredited laboratories.