Reproducibility of E-class weights

In the uncertainty of E-class weights the need is recognized for an additional component, termed reproducibility, that comes from a time dependence slower than that of the repeatability of the balance but shorter than that of the drifts in mass values that are sometimes seen. The observed scatter over times of the order of one year in the values of check weights is assumed to be due to the repeatability, which is calculable, and the reproducibility which can hence be found by subtraction. Values are given for weights used in this laboratory. The possible origin of this reproducibility uncertainty is discussed and the conclusion reached that it is not related solely to surface phenomena.