Like many calibration laboratories, our laboratory provides calibrations for a wide range of instrumentation. For the most part, we calibrate the instrumentation to the manufacturer's published specifications. As one of our services, we provide calibrations of electronic balances for customers within our company; the calibrations are performed at the customer's location. In our experience, most of our customers are not using their balance as a comparator, but simply putting an unknown quantity on the balance and reading the displayed value. Manufacturer's specifications for balances typically include specifications such as readability, repeatability, linearity, and sensitivity temperature drift; but, what does this all mean when the balance user simply reads the displayed mass value and accepts the reading as the true value? What is the uncertainty in the measurement? This paper discusses a method for assigning a direct-reading uncertainty to a balance based upon the observed calibration data and the environment where the balance is being used.
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