Class 0 calibration weights used as primary reference standards for calibrating other reference standards and weights and for calibrating microbalances. Class 0 weights have extremely small tolerances and should be used in extremely stable environments and
handled with the highest level of care. Otherwise, due to their one piece design, Class 0 weights will not maintain their measured value within the tolerance class. One may be tempted to purchase the weights with the tightest tolerances in order to reduce measurement uncertainty. However, frequency of use, care, handling and environmental conditions all play a major role in the long term stability of weights and these factors should be considered before purchasing Class 0 weights.