Can a multifunction calibrator really verify a long scale digital multimeter that is more accurate than the calibrator? This paper describes methods to characterize a multifunction calibrator to better than manufacturer’s 24 hour specification at all points that are used to verify 8.5 digit multimeters. Using automated processes, data collection and statistical methods, it was found that a calibrator can be characterized at all required values to uncertainties capable of verifying long scale DMMs. Sources of error that had to be overcome include thermal EMF, loading errors from the devices used to measure the calibrator output and loading errors from DMMs when measuring the characterized output. Data from repeated measurements of the calibrator shows 10 V will drift less than 0.3 µV/V for 30 days. For resistance, 10 k? can be shown to stay within 0.25 µ?/? for the same period. As the uncertainty of the calibrator was reduced, standards and techniques used to verify the multifunction calibrator had to be re-evaluated to decrease their uncertainty also.

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