Four years have elapsed since the prior calibration of the NIST working kilogram mass standards. A recent recalibration was performed using one of the new commercially-supplied super balances. These balances are being acquired by a surprising number of laboratories and their use brings to the fore some interesting issues.. Presented along with the 1994 recalibration results is a discussion bearing on the economic efficacy of these balances and problems they present the unwary metrologist; including density of weights, cleaning, uncertainty statements, OILM class E1 weight tolerance, apparent mass, etc.
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